New: _GetModFormFromModName()

- New function _GetModFormFromModName(): retrieves a mod's form object
when given the mod's name and the FormList it should look into. Useful
after the recent code change but contains a while-loop.
- Renamed _GetModNameFromFormList to _GetModNameFromModFormList.
WIP: Global RS Multipliers MCM page

- Begun work on Global RS Multipliers MCM page.
- Fixed a logical error in NPC Sync Mode Changes page affecting the
OptionFlags.