Undo & Redo should refocus to where changes are being applied

[dcht00]

Currently, Undo & Redo don't refocus to where they're performing changes. This, for big pads, unfortunately makes them practically unusable, and even dangerous (as you can't see what you're doing).

Behaviour in other editors:

• in gedit, cursor is moved
• in libreoffice, on redo, if it's an addition, it gets selected