Create transformers that allow specifying transformer actions on
specific libraries.
* angular2/transform/codegen: Generates all necessary code.
* angular2/transform/reflection_rewriter: Replaces `bootstrap` calls in
application entry points to remove transitive dart:mirrors import,
resulting in smaller code size & faster execution.
* angular2/transform/deferred_rewriter: Rewrites deferred imports and
`loadLibrary` calls to initialize Angular2 and preserve deferred
operation.
Proper configuration of these three transformers can replace the single
angular2 transformer, resulting in significant performance gains for
builds of large angular2 apps.
Update angular2 itself to declare the codegen transformer, since it has
neither deferred imports nor application entry points.
Remove the undocumented & unused quick_transformer.
