Ctlra Mapping: Prototype overlays

[harryhaaren]

Overlays will enable sections of a layer to be remapped, with a "fallback" to another layer. This allows re-coding a number of items without copy-pasting the whole block - which would become a maintenance nightmare. Thinking is to have a layer name for each layer, and specify a number of overlays that apply to a base-layer. Eg:

[layer.0]
name = base
overlay.0 = sliders_as_pan
button.0 = mappa:overlay_activate,sliders_as_pan
slider.0 = app:track_1_vol

[overlay.0]
name = sliders_as_pan
slider.0 = app:track_1_pan