picture Handling - save/parse XML done, git still missing

[Dirk Hohndel]

I just pushed a few more commits that make Subsurface compile again with
Qt5, that slightly change the picture data structure (it seems silly to
have a 64bit timestamp in there - and the code gets simpler (and the XML
easier to read) if we use an offset from the beginning of the dive
instead).

With this I have things working so the references to the images are stored
in the XML file and successfully read back.

As before, git handling is still missing and looking for a volunteer
contributor :-)

/D