mel rotomap-molepicker: add '--loop' arg
mel rotomap-molepicker: add '--loop' arg

Make it easier to pick lots of moles by allowing a 'loop' behaviour.
Users may still exit by pressing any other key.

Test Plan:
$ ./meta/run_tests.sh

.. in a rotomap dir ..
    $ mel rotomap-molepicker --images *.jpg
    .. prints UUID as usual and exits ..
    $ echo $?
    0

    $ mel rotomap-molepicker --images *.jpg --loop
    .. prints UUID after picking ..
    .. prints another UUID after picking ..
    .. prints another UUID after picking ..
    .. exits after 'q' is pressed ..
    $ echo $?
    0

aevri/mel,aevri/mel