feat(package): introduce a catch-all package angular.

modules/angular has no implementation, but depends on all the pieces
that make angular - core, di, directives, etc. It is the package that
all client apps will depend on.

tools/build/snippets/runtime_paths.js

@@ -1,4 +1,5 @@
 System.paths = {
+  'angular/*': '/angular/lib/*.js',
   'core/*': '/core/lib/*.js',
   'change_detection/*': '/change_detection/lib/*.js',
   'facade/*': '/facade/lib/*.js',