feat: location property

[mjspeck]

This has been a catchall for a couple things I noticed needed to be changed. The main differences are:

• I added location and unit properties to a lot of objects so that you can count on always having those two attributes in the appropriate classes. I didn't want to eliminate province attributes, even though I don't think they should exist, in order to maintain backwards compatibility
• I added and exhaustive_provinces attribute to DMZ arrangements to make it easier to list off all the locations. The comment should explain
• I moved daide_visitor.py to visitor.py.

[bpshaver]

Branch name does not follow <issue type>/<issue identifier>-<issue description> format :(