Changelog:
* Fixed letterboxing on PAL
* Add STATE_HELD for held button actions (eg: draggable elements)
* Now tracks state changes per-remote
* Default constructor for GuiImage
* Keyboard corrections, added more keyboard keys
* Better handling of multiple wiimote cursors on-screen
* Added functions for the ability to alter button behavior for all states
* Documented GuiTrigger class
* Refactor - moved trigger class definition to gui.h