Allow storing a preset to a user slot (RK)

[Paul-Dempsey]

from Richard Kram:

And a feature request: After loading a system preset with HC-1, allow HC-1 to put that in a defined user position slot.

I think right click for preset in any tab to offer option to store it to a user slot. Since we don't show the gaps, it will need to simply pick the first available empty slot.

Another idea is to have a display mode for the User tab that shows the empty slots and provide a menu option for a slot to copy the current preset to that slot.

I think it could even be possible to support rearranging presets in the User area, as long as there is a free slot to use as a temporary location.