Remember and default to last used screen area

If the grab screen area feature has been previously used, it should remember and default to that selection on subsequent uses.

## Problem

I want to take screenshots that will comprise a series (e.g., of a process that I’m documenting). I want all my screenshots to have the same dimensions and for elements within them to not jump around.

Currently, I have no way ensuring that any two selections I make are of the same coordinates and size.

## Proposal

The grab screen area mode should remember its previous location and dimensions and default to it.