Core options changes + update to v2

Updated core options to v2.
Not really needed here but updated "libretro.h".
Added a "Use Firmware Settings" option, for users who prefer to use language and username from the DS firmware.
Added a "Language" option.
Default username is now the one set in the frontend, if emtpy it will fall back to "melonDS" just like before.
Reduced the "JIT Block Size" max from "100" to "32", as it's the max allowed by the emulator anyway: https://github.com/libretro/melonDS/blob/6a03f3f11a729dbf698ec53954c735a0680aca01/src/ARMJIT.cpp#L579-L580
Adjusted the screen gap to a few fixed values to match standalone (but if people prefer, I'll re-add the 0 -> 192 options):
Made "Mouse" the new default for "Touch Mode", makes more sense than having it disabled IMO.
Show/hide OpenGL and JIT options depending on if they're enabled/disabled and Hybrid options depending on the selected layout.

I think that's it, please feel free to adjust and/or complete the options descriptions.

libretro / melonDS