[WIP] Add support for CSS encapsulation to transcluding components

WIP [DO NOT MERGE]

* Extract ComponentCssLoader so it can be shared by ShadowDomComponentFactory and TranscludingComponentFactory
* Implement a CSS transformer similar to the one provided by Platform.JS. A more full-featured compiler will be submitted as a separate PR.
* Rename EventHandler into ShadowBoundary
* Rename WebPlatform into WebPlatformShim and provide two implementations: one based on platform.js and the other one built into Angular.


TODO:
- [x] Refactor ShadowDomComponentFactory#call and TranscludingComponentFactory#call.
- [x] Test ShimmingViewCache in isolation. At the moment it is tested indirectly. 
- [x] Test the default shim
- [x] Fix #1300

Includes #1304 
Closes #1300
Why this change ?