Dive equipment edit - fix logic for applying changes

We keep getting this wrong. First you check all selected dives that are
not the current dive, make sure the equipment was the same before the edit
and then apply the changes. Then, when you are done with ALL of them, then
you change the current dive. Otherwise you cannot compare to the 'before'
state anymore.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Correctly track the 'changed' status of the equipment widgets

updateDive() cannot reset the changed status - this is called while the
dive is edited. Instead this status is reset when the user either accepts
or rejects the changes.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Improve handling of cylinders with identical gasmix

In reality we have no concept for handling those, yet. But the UI doesn't
prevent the user from entering multiple cylinders with the same gasmix, so
we need to help the user to get rid of them as well.

If the user attempts to remove a cylinder we check if there's a second
cylinder with the same gas. If that's the case then we can proceed and
remove the cylinder the user wants to get rid of without losing that gas
for the dive. The only tricky issue is that we need to make sure that if
we remove the first cylinder that one is actually replaced with one with
the same gas.

Fixes #622

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Fix the description of test dive cylinders

It is really confusing when the size of the cylinder does not match the
description. Inconsistent data in will mean inconsistent data out and
validating that export works means I try to get consistent data out...

Signed-off-by: Miika Turkia <miika.turkia@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Try to detect first cylinder on divelogs.de export

Most dive computers start always with the first cylinder (and if not,
they give a gas switch in the first few seconds). Trying to follow this
principle on divelogs.de export.

The bug 626 sounds like a bit different case so a sample XML log would
be needed to ensure that use case gets fixed.

See #626

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