Proposal: Aux Sends with matrix

Aux sends get a bit tricky when we're dealing with sidechain plugins. In some case it can be handled as described in https://sourceforge.net/p/qtractor/wiki/How%20To%20-%206%20Alternative%20Sidechain%20Workflow%20with%20Aux%20Sends/

Some constraints apply. For example the track must output to a 4 channel bus if you want to have Aux Sends to 4 channel buses. And you cannot change the order of the channels. Channel 1 of the track is always sent to channel 1 of the bus.

What if this restriction would be removed with a matrix belonging to each Aux Send? So it would be possible to have a 2 channel track that has an Aux Send to a 4 channel bus, e.g. like

Track ch 1 -> Bus ch 3

Track ch 2 -> Bus ch 4

Another track:

Track ch 1 -> Bus ch 1

Track ch 2 -> Bus ch 2

Sidechaining made easy!

This would open a new world of latency free routing inside Qtractor.