Conjureditemsgmstcheck

Resolving https://bugs.openmw.org/issues/1906

It adds a Flag_Bound flag that can be used against an ItemStack's mFlags member to quickly determine whether or not it is a bound item. 

Though the system that assigns the bit should probably be elsewhere (see: mwbase/world.hpp mwworld/worldimp.cpp /mwworld/worldimp.hpp). I just couldn't find a better place on my own, I tried adding code that'd allow for it to be done against Store<ESM::GameSetting> but the use of templates was causing more problems than I was solving going that route.