Libdivecomputer: start actually importing the dive data

So this actually reports the dive data that libdivecomputer generates.
It doesn't import special events etc, but neither do we for the xml
importer.

It is also slow as heck, since it doesn't try to do the "hey, I already
have this dive" logic and always imports everything, but the basics are
definitely there.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>