more flexible regex that validate the command coming from remote app

the [current regex that validate the command](https://github.com/ole-vi/bluetooth-server/blob/master/bluetooth-server.py#L41) on the raspberry pi side is somewhat "strict". It might limit the commands we could send on the remote side. 

Related to https://github.com/treehouses/remote/issues/22
Same as https://github.com/treehouses/remote/issues/46