There was this ugly pattern of passing pointers-to-dive_site via
a QVariant of void * type. This is of course inherently unsafe.
Pass these pointers using their proper types instead. This makes
it necessary to register them in Qt's meta-type system. Doing so,
fixes a bug: QML couldn't call into updateDiveSiteCoordinates()
because it didn't know the type and thus the coordinates of
the moved flag were not reflected in the divesite-dialog.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>