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"
```
This is the other major AC-specific change, although I could see this working for MAGFest. They only allow one dealer per table, and everyone else is a "Dealer Assistant"