Merge pull request #908 from ablake/next

Quick fix for ImageControl default regions.
Added public methods on ScriptController for registering and unregistering global script callback functions (i.e. initiailze, finalize, update, render, touchEvent, keyEvent, etc). Multiple registered functions per callback are now supported and scripts can register themselves.
Updated gameplay lua script bindings.
Merge pull request #910 from sgrenier/next

Added public methods to register global script callbacks
Fixes #866
Removing the erroneous if statement around drawing a control's background allows there to be
borders only on some sides of a skinned control.
Using NEAREST filter instead of LINEAR on theme textures to fix blurry borders.