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 lot of help came from @cantoine on this, in fact, wouldn't have been possible without him :)

Bonus fixes: Register and Unregister both caused node to error out.