Commands now save to the db

The commands now save to the database. Ironically enough, the code had channel.save() as opposed to commands.save(). Changing it to commands.save() works! This fix is for [Issue 28](https://github.com/UniBot/UniBot/issues/28). A ton of help came from @cantoine on this, which was very appreciated!

Bonus fixes: Register and Unregister both caused node to error out.