Add /mirror command support

[midspace]

Add the ability to mirror ships in game (symmetry) after a ship has been built.

[midspace]

The command works fine in single player, however on a server it is not syncing from the server to the clients.

If you disconnect from the server and reconnect, the new blocks will appear.

It appears to be an issue with the game API. I've raised a Discord ticket with Keen, SE-7786.