Feature: Add "rebuild" command to reconstruct map from existing channel data

[Tohaker]

Sometimes maps go stale and their images get deleted. We need to;

1. Keep the base map (remove any time constraints)
2. Keep the channel data if the base map is present (Janitor change, see Fix: Make sure Janitor can properly delete orphaned channel data #26 )
3. Allow the user to run a /map rebuild command to take the base map and apply all existing token info to it, replacing the current map with the new one.