Adds support for enabling / disabling MPD outputs

Adds support for binding switches to MPD outputs.

```
Switch Output1 { mpd="ON:player:enable=1, OFF:player:disable=1" }
Switch Output2 { mpd="ON:player:enable=2, OFF:player:disable=2" }
```

This requires an update to the binding config
```
mpd="<openHAB-command>:<player-id>:<player-commandLine>[=<player-commandLineParam][,<openHAB-command>:<player-id>:<player-commandLine>[=<player-commandLineParam]][,...]"
```