Better ways to select/deselect matrix cells

[Robert Leach]

I think that deselecting selection portions of the matrix might be able to be improved. Previously, a right-click would deselect. Recently, the ability to deselect by clicking nothing was added. That's a common feature for Adobe and I think that's good. But I think that we could also implement either:

1. Escape key = deselect all (which could be problematic given different functions of escape when different elements have focus - though we could allow the tab key to move focus to the matrix for keyboard controlls)
2. Command-a could select everything (or all that is visible?) and conversely, command-shift-a (in addition to command-d already implemented) could deselect everything
3. There are also options of click-modifier-drag to deselect a portion, but currently, only symmetrical selections are supported, so this could not be implemented (yet)

The specifics for modifier behaviors w.r.t. keyboard shortcuts and clicks & drags on the matrix, delineated in the holistic modifier plan in issue #70, should be followed.

[Robert Leach]

See related issue #264

[Robert Leach]

Removing milestone: Selecting Data (automated comment)