Recently we changed the MapLocationModel-items to store whether
they are selected. Thus, we can directly export an isSelected
flag instead of calling a function taking a dive-site argument.
1) This makes the QML easier to read.
2) This avoids passing pointers through QML which has caused
us lots of pain.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>