Correctly mark divelist changed after accepting dive plan

Commit 293126257b20 ("Mark divelist as changed if user accepts planned
dive") had the correct commit message but an incorrect implementation.

This moves the mark_divelist_changed() call into the GTK_RESPONSE_ACCEPT
clause where it belongs.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Add GFlow/GFhigh settings in dive planner

The planner interactively responds to changes to the GFlow and GFhigh in
the dialog and calculates an appropriate profile. If there is a previous
dive within the 48 hours prior to this dive then its saturation is
correctly taken into account if the gradient factors are changed - so if
they are aggressively lowered it is possible to start the dive with
already an existing ceiling (simply increase the surface interval to 'fix'
that).

Once the plan is accepted the GF values are reset to the current
preferences. This can cause the ceiling in the plot to change and the deco
stops to no longer match the ceiling - but that's a logical consequence of
the ability to change a temporary copy of GFlow/GFhigh during the planning
process and not the actual preferences (which would be counter intuitive,
I think).

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>