Messy restructuring & sixense controller detection

-Moved Xinput code into in_xinput.c
-Moved Sixense code into in_sixense.c
-Add initial support for detecting Sixense controllers
Cleanup for key event handling

-Can support more than 256 key events
-Removed hardcoded references to max number of key events
-Moved Xinput key events to 300+
Add key events for Sixense controllers