Resize the image in background

Decoding and resizing of the image is done in
Adapter-getView method which runs in the main
thread. As a result edit screen resumes after
few seconds, mean time if user flings on that
activity it leads to ANR.

From getView method, adopt lazy loading - spawn
the thread which will decode and resize the
image, upon receiving the requested resized-image
set the image to the view.

Change-Id: I7500afc2fcc4fd7bed8f256d19cbc22ee9baeda0
CRs-Fixed: 550421