FEATURE: replace the gmic plugin with the gmic-qt plugin

To make this work, you have, for now, to build the gmic-qt plugin
from https://github.com/boudewijnrempt/gmic-qt . The gmic people
will hopefully create binaries of the gmic-qt plugin for Krita
with the next release :-)

CCMAIL:kimageshop@kde.org
CCMAIL:david.tschumperle@gmail.com