UI Changes:
- Added default UI theme to gameplay/res/ui, which is copied into sample folders.
- Optimized UI layout code (still in progress).
- Removed AUTO_SIZE_STRETCH in favor of width=100% and height=100%.
- Changed all controls to default to autoSize=AUTO_SIZE_BOTH, which automatically sizes controls to tightly fit their contents. This greatly simplifies UI creation since explicit sizes are no longer required.
- Updated samples to reflect the above mentioned changes to auto-sizing.
- Cleaned up a lot of UI code (still more to do).
- Updated lua bindings.