refs #3812. Add TAB to list of ignored keys for undo handling.  This should complete necessary changed for basic editor a11y but waiting to close ticket until further testing and review.
refs #3812. Add TAB to list of ignored keys for undo handling.  This should complete necessary changed for basic editor a11y but waiting to close ticket until further testing and review.

git-svn-id: 674a2d6b1e32e53f607eb824547723f32280967e@10556 560b804f-0ae3-0310-86f3-f6aa0a117693

redaktor/deliteful