Label Channels in Mixer Plugins

[v322v322]

It would be nice to be able to label the channels in the mixer plugins. It is a bit tedious having to flip to the Carla or QJackctl patchbay view to see what each mixer input is. If you do add this, please make sure the labels get stored with the save data. It would also be good if the plugin JACK inputs would change to match (for stereo channels, make it channelName-l and channelName-r or whatever the first letters are for the words "left" and "right" in the language it is running in)