Add support for flag/trigger groups to monsters and species definitions

This adds a new type (TAG_GROUP) which is used to group commonly occurring sets of tags together. As a proof of concept I grouped "SEES", "HEARS", "SMELLS" flags together into a tag group with the id: "F_SEE_HEAR_SMELL"; references of that exact order in monsters.json were changed to the tag group's id for testing. The flags were loaded successfully. This can be used for both flags and triggers.