[New feature] Create a complete, "libre" tagset

[SnowyMouse]

Currently, building maps requires that you either...

• use existing content, almost always owned by Microsoft or Gearbox, or
• make every tag yourself

The Halo Editing Kit comes with its own tagset. This tagset is a base set of tags that is commonly present in the game's included multiplayer maps and is enough to build one map: tutorial.map.

Ideally, we should have a tagset that people can use to create their own playable maps without requiring it to be attached to the Halo IP. Something like this should include:

• ui, singleplayer, and multiplayer menu tags
• a complete multiplayer globals tag
• a complete sandbox with weapons, vehicles, and equipment
• a few skyboxes for people to choose from
• some scenery for people to choose from
• a simple level that is playable on all gametypes

This requires literally everything tool-related to be finished first, but doing this will be useful.

In regards to installing, this should be optional.