Drop the decode lock on stream handling.

This lock was actually detremental to the speed since we piped streams directly to the Bitmap decoder rather than through an intermediary byte array. Thus we potentially blocked all bitmap decoding while waiting on a single stream.

Only lock decoding from Bitmap to Bitmap since that is where the real potential to OOM exists.

Closes #49.
Merge pull request #57 from square/jw/pop-lock-and-drop-it

Drop the decode lock on stream handling.
Add support for contact photo loading.
Add contact photo loading sample.
Do not attempt to load Uris which point directly at a contact photo.
Add tests for the contact photo loading code paths.
Merge pull request #56 from square/jw/uri

Add Support for Contact Image Loading
Use Uri to handle resources loading.

It kills resourceId param and field everywhere.
Add support for loading images from assets

Images can be loaded from assets using a special type of Uri (e.g.
assets:/image.png)