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 an AC-specific change - AnthroCon doesn't have a separate price for dealers, so we can't use the dealer_badge_price.