Mixer selection follows mouse
This eliminates ambiguity about which strip the keybindings will affect.
Hold shift to make a quick group from adjacent mixer strips.
holding Primary(ctrl/cmd) allows user to make noncontiguous strip selections
holding Primary(ctrl/cmd) allows user to make noncontiguous strip selections
Allow deletion of processors in editor_mixer_strip by pointing and pressing Delete
This had to be hacked because the editor_mixer strip is on the editor and doesnt respond to mixer keybindings.
Also force the gain intry to lose focus if the user leaves the mixer strip.  this will probably solve some long-standing complaints.  although perhaps a more elegant solution is possible.