scripts/get_maintainer.pl: add interactive mode

This is a first version of an interactive mode for
scripts/get_maintainer.pl.

It allows the user to interact with the script.  Each cc candidate can be
selected and deselected and a shortlog of authored commits can be
displayed for each candidate.

The menu is displayed via STDERR, the end result is outputted to STDOUT.
This unusual mechanism allows using get_maintainer.pl in interactive mode
via git send-email --cc-cmd.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>