Replace UUIDs by pointers to dive-site in mobile code. In both
cases, the value is transported via a QVariant. The function
getCoordinatesForUUID(), which was only used from mobile, can
be replaced by a getCoordinatesFor() function taking a variant
supposed to contain a dive-site pointer. Likewise, the variant
of the centerOnDiveSite function is now supposed to wrap a
pointer-to-divesite.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>