Change edit shortcut from 'm' to 'e'

I keep missing the shift key when typing shift-m to mark a file
as reviewed and move to next file. With 'm' bound to open file in
editor this is launching me into the edit screen, which is annoying
to get out of.

Swap to 'e' which is currently not bound to anything.

Change-Id: Ia92e1b71cda34bd7d5fd77e8d0423670114e1a0c
(cherry picked from commit cb9cc54762c70229615a6dba4d462ad1aa5cc43f)