Add a button to enable a piano-roll TCO

Enhancement:
We have **all** done this:
Dobble click a TCO pressed play, and had -no- replay..
Yes the track is muted..
So the 'fix' is to
* close this piano-roll
* find the track in question in song-editor
* enable the track
* re-locate the TCO in question
* open that (by now free¤%%#) piano-roll

Because of *that* i suggest a diode inside piano-roll, that will enable replay-Something like

Start by locating the piano-roll and song-editor entry points, then trace how a muted track affects replay of its TCO. Done means the piano-roll provides a control that enables the relevant track so the TCO can replay without closing the editor.

Written by the indexing model from the issue text.