TE: Allow more flexible sector multi-selection

[Nickelony]

Allow the user to select sectors more than once (with CTRL+Click).

This means in a sequence of sectors like:

1, 2, 3, 4, 5

We should allow the user to select just 1, 3, 5, without 2 and 4

I think this would be great, but we would have to prevent the user from using any group-based tools like "Ramp Tool", "Dome Tool" or "Pyramid Tool" when this type of multi-selection is used, essentially only making the most basic tools work with it, such as Brush, Pencil, Drag tool etc.