Store/Fetch Message Command

[MaZderMind]

For external UIs which have their own distinct state (ie. Voctoknopf), a Command is needed which stores and holds a Message for that kind of device.

The following Commands would be used to access it:

> store_message foo moo bar lala {'my':'content'} 42
< message foo moo bar lala {'my':'content'} 42          (broadcast)

> fetch_message foo
< message foo moo bar lala {'my':'content'} 42