* RequestFlag function, commit for posterity

This will actually be removed again, as we're ditching item flags for
the PrimaryHand group, but I wanted to commit it in case I need
something similar to do logic on whether a form can be set for hand X.
* Stripped itemFlag-related code, see FIXME
* Initial support for primaries and group icons
* Refactor and handle MH flag in onGroupUse
* Rewrote most of OnGroupUse event

Made dual-wield weapon equip much more reliable
Implement new SKSE EquipSlot form for spells.
Replaced HandSlot system with more accurate tracking of rHand, lHand,
and Voice slots
If one-handed spell is equipped and other hand is empty, dual-wield the
spell