Add random encounters

[Standing-Storm]

I added random encounter infrastructure to Xedra Evolved/XedraWood, time to add it to Arcana.

• Add a group of briarwitches doing a ritual in the deep woods that you can stumble onto.
• Add a couple members of the Cleansing Flame fighting some monsters

I tested it and it all works but I can't merge it yet because creature_remove is broken in DDA