Fix time zone conversions

I know I tested this - no idea how I missed this.
Anyway, this was of course utterly bogus. Whenever we get a time from a
time_t into a Qt Date or Time datastructure, we need to adjust it by the
timezone offset as otherwise Qt will assume it's in local time and
helpfully change it to the wrong values for us.

See #655

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Retain the start time when creating plan from dive

We need to make sure that the start time is set before we start adding
points.

Fixes #661

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Change the Ruler text values when metric system changes.

"ups", as I did this in Metric system I forgot to update
to imperial when the user selected it.

Fixes #665

Signed-off-by: Tomaz Canabrava <tomaz.canabrava@intel.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>