Widget size policy, size callbacks

-> vertically resizable widgets behave are sized to fill
-> non-vertically resizable widgets use the small size all the time
-> providing size call-backs. ensuring that we don't send excessive /
   incorrect size callbacks. These are expensive. Had to clean things
   up to ensure we only send the truth, and not bounce around.

Change-Id: I8038de01096906526e2622c6f1cd24c171e3a4ec