Allow disjoint manual selections with modifier key (command and/or shift)

[Robert Leach]

Since you can get multiple disjoint selections via searching and since we're planning on allowing users to copy or export selected data, I think it would make sense to allow them to select multiple disjoint areas. It's debatable whether we should allow or even force selections to be symmetrical (as you would get from a wildcard search), i.e. if a disjoint selection of a second contiguous area is made, either additionally select the cells of the intersection of the selected rows & columns or just show what they selected, but copy/export all intersections (or leave as empty tabbed columns).

I'll post a screen shot to demonstrate what I mean if that doesn't make sense...

Note that this issue should be implemented in a way that is consistent with the holistic modifier plan & cheat-sheet in issue #70.

[Robert Leach]

See issue #264 for thoughts on modifiers to select anew, add select, subtract select, toggle select. Also, if we allow multiple disjoint selections, the symmetrical-ness of the intervening areas can be either relative to the existing selection, the currently visible data, or the entire matrix. And there can be modifier keys to control that.

[Robert Leach]

Note that this issue should be implemented in a way that is consistent with the holistic modifier plan & cheat-sheet in issue #70.

[Robert Leach]

Removing milestone: Selecting Data (automated comment)