refactor(build): explicitly mention src folder in imports

Export files are now directly under the module folder,
e.g. `core/core.js`. With this, an import like `core/core`
won’t need a path mapping (e.g. via `System.paths`) any more.
This adds the `src` folder to all other import statements as well.

tools/build/snippets/runtime_paths.js

@@ -1,17 +1,4 @@
 System.paths = {
-  'angular/*': '/angular/lib/*.js',
-  'core/*': '/core/lib/*.js',
-  'change_detection/*': '/change_detection/lib/*.js',
-  'facade/*': '/facade/lib/*.js',
-  'di/*': '/di/lib/*.js',
-  'directives/*': '/directives/lib/*.js',
-  'rtts_assert/*': '/rtts_assert/lib/*.js',
-  'test_lib/*': '/test_lib/lib/*.js',
-  'reflection/*': '/reflection/lib/*.js',
-  'benchpress/*': '/benchpress/lib/*.js',
-  'examples/*': '/examples/web/*.js',
-  'e2e_test_lib/*': '/e2e_test_lib/lib/*.js',
-  'benchmarks/*': '/benchmarks/web/*.js',
-  'benchmarks_external/*': '/benchmarks_external/web/*.js',
+  '*': '/*.js'
 };
 register(System);