feat(animation): Animation library and demo application for Angular

Rough cut of animate service implementation, demo application under demo/animate_demo/index.html

Demo currently includes:
* `ng-if` example that animates css opacity and height animation.
* Animated box using the Animate service with `animate.addCss()` and `animate.removeCss()`
* 1,000 Animated elements running at the same time using the `Animate` service with `animate.addCss()` and `animate.removeCss()`.

Animation library currently includes:
* `window.requestAnimationFrame` based `AnimationRunner` implementation instead of timer delay for the animation loop.
* Extendable `Animation` interface for hooking up custom animation implementations.
* `CssAnimation` implementation for managing the state lifecycle of css class based animations.
* No-op implementation of the animate service for performance critical implementations.
* Integration with `ng-if`, `ng-unless`, `ng-show`, `ng-hide`, `ng-repeat`, `ng-switch`.

Notes:
* This adds a dependency on quiver.dart (Maintained by the dart team) for `Clock` and `BiMap<K, V>`.