Allow backspace to delete an empty child node/hide "+" button

[taramk]

to repro:
create a node
create a child node
backspace through the child node to try to delete it - you can remove the text and i suppose delete the node, but the empty + button is still there. when i backspace. it should remove/collapse/hide that plus button and put the cursor at the end of the node above.

http://recordit.co/0hvRlnJOKW