New command blackbox_edit

Hey,

I just created ```blackbox_edit``` which does both *_edit_start* and *_edit_end* commands in a fresh tempfile,I think it's handier than doing each step in separate.

I did not test it roughly, though, it's the minimal implementation to work on my machine. Also, it's not very DRY (I'm not used to shell scripts), so any feedback is appreciated.