Cleanup some of the sample app code
Refactor example to handle fragments correctly

Should fix case where searches would complete
but no photos would be shown
Convert flickr sample to use Volley
Expose downloader and volley request queue
Synchronous StreamOpener -> Async StreamLoader

An extensive but relatively minor change to the
internal interfaces to allow for asynchronous 
InputStream opening in the ImageManager. This
allows us to use async http libraries (like 
Volley) without forcing us to always start a 
download and then check the ImageManager cache
only after the download completes.
Update the flickr sample for the new interface
remove volley sumodule from flickr sample
Add Volley as a submodule of Glide
Make Volley default Model/Stream loader for http
Use Glide's Volley api in flickr sample
Gracefully handle search failure in flickr sample
Run resize tasks in our thread pool

Previously would have run them on whatever thread
the callback was called on, which may have been
some external library's thread.
Update the comments in the Glide singleton
Gracefully handle search failure in flickr sample
Update the comments in the Glide singleton
Add a BaseModelLoader

Allows us to remove the repetitive
ModelLoader.close() -> StreamOpener.cancel()
Clear loaders before load in ImagePresenter

Allows us not to call clear before new loads in
all of the loaders
update VolleyModelLoader to remove repeated code
Simplify the exception handler in ImagePresenter
Make compression quality to diskcache configurable

Also decrease the default from 100 to 90.