Multi-instance support

Only works in the GUI for now, doesn't break  the command-line client but the new options are not implemented.

Related to #29 
Uh oh, I have no idea what we're enabling here. In fact, I can't even find an `Enabled` variable that appears to be in scope here. Is this defined in another file? What does it mean for `Main()` to be enabled?

- [ ] Make pjf less confused.