PicoDrive, XMB assets, BIOS template, various fixes
Changes:
- A lot of FDS fixes and shell optimizations
- Added PicoDrive core
- Removed mupen64plus core (it's too slow)
- Added XMB assets module
- Respect custom aspect ratio setting in retroarch.cfg
- Added BIOS module template
- Reverted mGBA core back to build from BuildBot (savestates issues)