[Cin] MKV containers

[Andrea paz]

To deal with Cin's different operating philosophy compared to other
editors, the first hurdle is to understand that it works on the tracks
in their entirety and not on individual edits. Recently, "fast drag"
has been introduced to make it more similar (and comfortable) to other
editors. But it remains the basic concept of enabling and disabling
tracks according to the need of the moment. "Shift + click" on the arm
button in the patchbay, enables the track disarming all others.