build(aio): big move of docs related files (#14361)

All the docs related files (docs-app, doc-gen, content, etc)
are now to be found inside the `/aio` folder.

The related gulp tasks have been moved from the top level
gulp file to a new one inside the `/aio` folder.

The structure of the `/aio` folder now looks like:

```
/aio/
  build/         # gulp tasks
  content/       #MARKDOWN FILES for devguides, cheatsheet, etc
    devguides/
    cheatsheets/
  transforms/    #dgeni packages, templates, etc
  src/
    app/
    assets/
    content/    #HTML + JSON build artifacts produced by dgeni from /aio/content.
                #This dir is .gitignored-ed
  e2e/           #protractor tests for the doc viewer app
  node_modules/ #dependencies for both the doc viewer builds and the dgeni stuff
                #This dir is .gitignored-ed
  gulpfile.js   #Tasks for generating docs and building & deploying the doc viewer
```

Closes #14361

aio/transforms/angular.io-package/processors/addNotYetDocumentedProperty.spec.js

@@ -0,0 +1,148 @@
+var testPackage = require('../../helpers/test-package');
+var Dgeni = require('dgeni');
+
+describe('addNotYetDocumentedProperty', function() {
+  var dgeni, injector, processor, log;
+
+  beforeEach(function() {
+    dgeni = new Dgeni([testPackage('angular.io-package')]);
+    injector = dgeni.configureInjector();
+    processor = injector.get('addNotYetDocumentedProperty');
+    log = injector.get('log');
+  });
+
+  it('should mark export docs with no description as "not yet documented"', function() {
+    var a, b, c, d, a1, b1, c1, d1;
+    var docs = [
+      a = {id: 'a', docType: 'interface', description: 'some content'},
+      b = {id: 'b', docType: 'class', description: 'some content'},
+      c = {id: 'c', docType: 'var', description: 'some content'},
+      d = {id: 'd', docType: 'function', description: 'some content'},
+      a1 = {id: 'a1', docType: 'interface', description: ''},
+      b1 = {id: 'b1', docType: 'class', description: ''},
+      c1 = {id: 'c1', docType: 'var', description: ''},
+      d1 = {id: 'd1', docType: 'function', description: ''}
+    ];
+
+    processor.$process(docs);
+
+    expect(a.notYetDocumented).toBeFalsy();
+    expect(b.notYetDocumented).toBeFalsy();
+    expect(c.notYetDocumented).toBeFalsy();
+    expect(d.notYetDocumented).toBeFalsy();
+
+    expect(a1.notYetDocumented).toBeTruthy();
+    expect(b1.notYetDocumented).toBeTruthy();
+    expect(c1.notYetDocumented).toBeTruthy();
+    expect(d1.notYetDocumented).toBeTruthy();
+  });
+
+  it('should mark member docs with no description as "not yet documented"', function() {
+    var a, a1, a2, b, b1, b2, c, c1, c2;
+    var docs = [
+      a = {
+        id: 'a',
+        docType: 'interface',
+        description: 'some content',
+        members: [a1 = {id: 'a1', description: 'some content'}, a2 = {id: 'a2', description: ''}]
+      },
+      b = {
+        id: 'b',
+        docType: 'class',
+        description: '',
+        members: [b1 = {id: 'b1', description: 'some content'}, b2 = {id: 'b2', description: ''}]
+      },
+      c = {
+        id: 'c',
+        docType: 'class',
+        description: '',
+        members: [c1 = {id: 'c1', description: ''}, c2 = {id: 'c2', description: ''}]
+      },
+    ];
+
+    processor.$process(docs);
+
+    expect(a.notYetDocumented).toBeFalsy();
+    expect(b.notYetDocumented).toBeFalsy();
+    expect(c.notYetDocumented).toBeTruthy();
+
+    expect(a1.notYetDocumented).toBeFalsy();
+    expect(a2.notYetDocumented).toBeTruthy();
+    expect(b1.notYetDocumented).toBeFalsy();
+    expect(b2.notYetDocumented).toBeTruthy();
+    expect(c1.notYetDocumented).toBeTruthy();
+    expect(c2.notYetDocumented).toBeTruthy();
+  });
+
+
+  it('should mark constructor doc with no description as "not yet documented"', function() {
+    var a, a1, b, b1;
+    var docs = [
+      a = {
+        id: 'a',
+        docType: 'interface',
+        description: '',
+        constructorDoc: a1 = {id: 'a1', description: 'some content'}
+      },
+      b = {
+        id: 'b',
+        docType: 'interface',
+        description: '',
+        constructorDoc: b1 = {id: 'b1', description: ''}
+      }
+    ];
+
+    processor.$process(docs);
+
+    expect(a.notYetDocumented).toBeFalsy();
+    expect(b.notYetDocumented).toBeTruthy();
+
+    expect(a1.notYetDocumented).toBeFalsy();
+    expect(b1.notYetDocumented).toBeTruthy();
+  });
+
+
+  it('should not mark documents explicity tagged as `@noDescription`', function() {
+    var a, a1, a2, b, b1, b2, c, c1, c2;
+    var docs = [
+      a = {
+        id: 'a',
+        docType: 'interface',
+        description: 'some content',
+        members: [
+          a1 = {id: 'a1', description: 'some content'},
+          a2 = {id: 'a2', description: '', noDescription: true}
+        ]
+      },
+      b = {
+        id: 'b',
+        docType: 'class',
+        description: '',
+        members: [
+          b1 = {id: 'b1', description: 'some content'},
+          b2 = {id: 'b2', description: '', noDescription: true}
+        ]
+      },
+      c = {
+        id: 'c',
+        docType: 'class',
+        description: '',
+        noDescription: true,
+        members: [c1 = {id: 'c1', description: ''}, c2 = {id: 'c2', description: ''}]
+      },
+    ];
+
+    processor.$process(docs);
+
+    expect(a.notYetDocumented).toBeFalsy();
+    expect(b.notYetDocumented).toBeFalsy();
+    expect(c.notYetDocumented).toBeFalsy();
+
+    expect(a1.notYetDocumented).toBeFalsy();
+    expect(a2.notYetDocumented).toBeFalsy();
+    expect(b1.notYetDocumented).toBeFalsy();
+    expect(b2.notYetDocumented).toBeFalsy();
+    expect(c1.notYetDocumented).toBeTruthy();
+    expect(c2.notYetDocumented).toBeTruthy();
+  });
+});