This required a bit more untangling, but with this it seems we can build
subsurface-mobile again (at least on the desktop).
Interesting is the removal from inside the ImageDownloader of the call to
DivePictureModel::instance()->updateDivePictures() - which actually could
cause some interesting recursion issues. If it turns out we did indeed
need this, it needs to be re-architected.
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
