Don't use a special downsampler in ImageManager

It doesn't work for non exact sizing.
Merge branch 'fix_problem_decoding_from_disk_cache'
Make SafeKeyGenerator thread safe.
Fix bitmaps too large for memory cache being added to pool too soon.
Increase the default cache size and default to internal cache dir.
Use small memory cache and large bitmap pool on new and non low ram devices.
Decrease the default number of threads glide uses to resize images.
Add debug logging for exceptions loading images.
Add more robust view size detection.

Includes at least functional support for 
wrap_content.
Make model loaders and decoders generic.
Add basic support for decoding video thumbnails
Handle videos and images in one request.
Revamp Glide interface to be more flexible.

Conflicts:
	library/src/com/bumptech/glide/presenter/target/ImageViewTarget.java
Don't attempt to reuse ImagePresenters in top level interface.

Change-Id: Ic8c82958c4b0e28c6d1df3d950901be034cbc7e3
Fix NPEs with optional loaders in BaseBitmapLoadTask.

Change-Id: I4cfec042db8bb30318f61c396853d75d06a7d2f7
Add convenience methods for retrieving common model loaders.

Change-Id: Ia83a51f9a8e32363e27af35493c947f1757cd8a6
Don't test removed functionality.
Use getWidth/getHeight in SimpleTarget
Bring back special handling for views using setTag
Add a more efficient fitCenter method.