Refactoring sqlite import support

Move the opening of DB connection to occur before DC dependent code.
This way we can try to detect log software before calling the DC
dependent import function. This prepares for adding support for
Shearwater sqlite database.

Signed-off-by: Miika Turkia <miika.turkia@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Import Shearwater Desktop divelog database

Sqlite database from Shearwater Desktop log software is imported. Just
the basic information like location, buddy, notes and dive profile
(depth and temperature).

This is tested with a DB in Imperial units, thus metric input might
contain errors.

Signed-off-by: Miika Turkia <miika.turkia@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Import gas info for Shearwater Desktop

Used gas mixes and gas changes are imported. Also po2, ndl, cns and
ceiling are added to profile samples. As far as I can tell, the Searwater
Desktop shows ceiling in 3 meter (or feet equivalent) steps, but stores in feet
(or probably meters). I just use the value reported, no conversion to 3 meter
steps.

Fixes #432

Signed-off-by: Miika Turkia <miika.turkia@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>