Allow resources to skip memory and disk caches.

Conflicts:
	library/src/test/java/com/bumptech/glide/load/engine/EngineJobTest.java
Add types to base and simple targets
Add GifDecoder and GifResource*
Add drawable request builder to handle image/video/gifs.
Make gif resources safe for multiple consumers.
GifBitmap -> GifBitmapWrapper
Code cleanup
Add timing logs for runners.