Request Resized Images From Plex Server

This greatly improves the speed of image downloading.

Also, when changing the background of the TV Grid, post a delayed task for 500ms
and cancel it if the item selection changes.
This improves the experience when moving around quickly in the grid because
it only loads the BG image when you pause for over 500ms
Don't Reload in onResume

Because the selected item is lost. Need to find a proper way of making
the grid view refresh. Probably in onActivityResult.
Merge pull request #217 from alonalbert/RightSizeImages

Request Resized Images From Plex Server
Merge pull request #219 from alonalbert/Reloead

Don't Reload in onResume
Merge remote-tracking branch 'upstream/develop' into develop