Improved debugger, modules and the SPU interpreter

Modules:
- Image decoding modules improved
- sys_fs module improved

Debugger:
- Keypress event listener in the instruction list
- Instruction editor added (key 'E')
- Register editor added (key 'R')

PPC Thread:
- Two virtual functions to read and write registers using wxString's as IO arguments: ReadRegString and WriteRegString

SPU Interpreter:
- New Floating-point instructions