#5 UX -5 -Bracket backspace

[Jack Mullaney]

When cursor is inside an empty bracket, the backspace key should delete the bracket. When the empty bracket is inside another empty bracket, the outer bracket's blue-dashed rectangle should be restored when the inner bracket is deleted.

[Kashif Imran]

Fixed the problem using two stage delete i.e. on first backspace the selection is marked for deletion (and shows a changed color). On second backspace it is deleted.