Connect MIDI (#201)

Okay, I've done some refactoring, mainly to protect against spammy connection attempts.

The main open issue is the connection between the `bpm` command and the new code here. I think we need both ways:

- `pulse` and `beat` should respond to `bpm` setting if there is no connection
- `bpm` should be set when there is a connection

In regards to the latter, I think it would be nice to do a replace on the entered number, in stead of `bpm pulse.bpm`. A changing number immediately gives the user a nice quantitative indication of the current BPM from the feed. If the user wants to unlock the BPM, she should just disconnect from the server (for which there is currently no way, which is the other issue).