Rotary (knob) Widget and MIDI Mixer Window

   Just pushed some improvements to the Rotary widget which provides the 
knobs that you see in various places in the UI.  The tool tip now shows 
what the knob is for (e.g. pan) and its value.  Previously a click was 
required to get the value, and no other details were provided.

   Did some cleanup work on the MIDI Mixer Window as well.  Studio > 
MIDI Mixer Window.  Should pretty much work the same.  Resizing is no 
longer allowed since it just spreads the widgets out.  This will 
hopefully be fixed for 25.12.

   Please test latest git.

   This work is in preparation for fixing bug #1677: Mixers don't 
visually scale.

Ted.