Add memory limited bitmap pool
Default to SizedBitmapPool

Also unify builder interface re bitmap pool so
it matches memory and disk cache (either default,
an implementation, or disabled)
SizedBitmapPool -> LruBitmapPool
do bitmap ref management on a bg thread

Reduces the number of locks the main thread needs
to acquire and the amount of time they need to be
held (as well as the contention for said locks)
Create a simple static interface for Glide

Allows most of the functionality of the library
without having to directly create and manage an
ImageManager and ImagePresenters.

Doesn't currently allow for all functionality and
is somewhat less efficient because it encourages
allocations of unneeded objects, but it is easier
to use and should cover enough cases to be useful.
Use the static Glide interface in the flickr demo
Simplified ImageManager singleton for Glide
Remove replace and build methods from Glide