Button expander

[danngreen]

Adds support for Button Expanders

The button lights and button itself are separate entities in the patch file, but the GUI should help keep them in sync (perhaps an override can be done to choose any LED to map to)

TODO:

• Allow mapping to the buttons in MM. GUI thread needs access to metaparams.button_events
• When creating a mapping in MM, determine the light to map to:
  • Check the module's info struct, see if the param element has counts.num_lights > 0
  • If not, then scan elements for one with counts.num_lights > 0 and an intersecting box (x/y_mm + width/height_mm)
• When removing a button mapping, remove the light mapping as well
• Add Button Expander to VCV
• Allow mapping to buttons in VCV
• Allow mapping lights
  • scan module's lightInfo's and look for one whose box intersects the param's box
  • Also add right-click menu so the user can select a different light on the module: just let the use pick a number from 1 to lightInfo.size(). Users can try one and see if they like it.

Future ideas to consider (create issues when closing this if we want to purse these):

• Mapping a button to an RGB button can take the average of RGB elements and turn on if they are over a threshold
• Allow user to choose which light to map to (including average of multiple lights)