git-codereview: add interactive mode to submit

This adds a -i option to submit that brings up a list of commits to
submit in an editor (a la git rebase -i), lets the user edit the list,
and then submits the specified commits in the specified order.

Change-Id: I88149140527c987ae856aac2598f0a992fe5654d
Reviewed-on: https://go-review.googlesource.com/16677
Reviewed-by: Andrew Gerrand <adg@golang.org>
5 files changed