AC Dealer changes

Includes all the changed logic to match AnthroCon's dealer system.

*Includes schema changes.*
New column: table_extras in Group table. This is a MultiChoice column.

*Includes configuration changes.*
New configuration under [enums]:
```
[[table_extra]]
power_table = "Powered Table"
wall_table = "Wall/Endcap Table"
```
Oh, awesome! I originally wrote something like that for loop, except I forgot to use `items()`. When it didn't work, I went to this version as a backup.

I'll implement this version next time I'm working on the code.