Synchronize with obspy mopad

For historical reasons, obspy ships it's own mopad version (https://github.com/obspy/obspy/blob/master/obspy/imaging/scripts/mopad.py). The two versions diverged quite a bit, which can be seen in this pull request, where I simply overwrote the geophysics/MoPaD version with the obspy MoPaD version: 3257 additions and 3161 deletions (unfortunately github does not show the diff, but they are easily visible locally).

Is there any plan for unification, such that obspy could include MoPaD as a submodule?

There were some performance improvements, bug fixes in the obspy version. Really merging the versions not by simply overwriting the one or the other, could be a tough task. Obspy.imaging also ships tests for MoPaD.

References:
 * discussion on this subject in the obspy repo https://github.com/obspy/obspy/commit/47019b4
 * obspy issue for MoPaD submodule https://github.com/obspy/obspy/issues/421