[Core options text] Text fixes

[IlDucci]

• Changing the main category sublabels to follow RetroArch's style.
  • Changed the "FS" part of the FBX NES Classic palette to "(fixed)" (FS meant fullscreen, as in, FBX did one version of this palette, but said themselves that it was captured incorrectly, so the fixed solution was captured by taking into account the parameters of the full screen. FBX never meant to have a full name for the corrected version).
  • One minor fix.