Add time stamp to the debugging printout of vendor specific samples

They are useful for debugging things in libdivecomputer and this way it's
easier to match the data to specific points in the dive profile.

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

This commit makes deco handling in Subsurface more compatible with the way
libdivecomputer creates the data. Previously we assumed that having a
stopdepth or stoptime and no ndl meant that we were in deco. But
libdivecomputer supports many dive computers that provide the deco state
of the diver but with no information about the next stop or the time
needed there. In order to be able to model this in Subsurface this adds an
in_deco flag to the samples. This is only stored to the XML file when it
changes so it doesn't add much overhead but will allow us to display some
deco information on dive computers like the Atomic Aquatics Cobalt or many
of the Suuntos (among others).

The commit also removes the old event based deco code that was commented
out already. And fixes the code so that the deco / ndl information is
stored for the very last sample as well.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Allow overlapping (and disjoint) dive trips

We used to have the rule that a dive trip has to have all dives in it in
sequential order, even though our XML file really is much more flexible,
and allows arbitrary nesting of dives within a dive trip.

Put another way, the old model had fairly inflexible rules:

 - the dive array is sorted by time

 - a dive trip is always a contiguous slice of this sorted array

which makes perfect sense when you think of the dive and trip list as a
physical activity by one person, but leads to various very subtle issues
in the general case when there are no guarantees that the user then uses
subsurface that way.

In particular, if you load the XML files of two divers that have
overlapping dive trips, the end result is incredibly messy, and does not
conform to the above model at all.

There's two ways to enforce such conformance:

 - disallow that kind of behavior entirely.

   This is actually hard.  Our XML files aren't date-based, they are
   based on XML nesting rules, and even a single XML file can have
   nesting that violates the date ordering.  With multiple XML files,
   it's trivial to do in practice, and while we could just fail at
   loading, the failure would have to be a hard failure that leaves the
   user no way to use the data at all.

 - try to "fix it up" by sorting, splitting, and combining dive trips
   automatically.

   Dirk had a patch to do this, but it really does destroy the actual
   dive data: if you load both mine and Dirk's dive trips, you ended up
   with a result that followed the above two technical rules, but that
   didn't actually make any *sense*.

So this patch doesn't try to enforce the rules, and instead just changes
them to be more generic:

 - the dive array is still sorted by dive time

 - a dive trip is just an arbitrary collection of dives.

The relaxed rules means that mixing dives and dive trips for two people
is trivial, and we can easily handle any XML file.  The dive trip is
defined by the XML nesting level, and is totally independent of any
date-based sorting.

It does require a few things:

 - when we save our dive data, we have to do it hierarchically by dive
   trip, not just by walking the dive array linearly.

 - similarly, when we create the dive tree model, we can't just blindly
   walk the array of dives one by one, we have to look up the correct
   trip (parent)

 - when we try to merge two dives that are adjacent (by date sorting),
   we can't do it if they are in different trips.

but apart from that, nothing else really changes.

NOTE! Despite the new relaxed model, creating totally disjoing dive
trips is not all that easy (nor is there any *reason* for it to be
easty).  Our GUI interfaces still are "add dive to trip above" etc, and
the automatic adding of dives to dive trips is obviously still based on
date.

So this does not really change the expected normal usage, the relaxed
data structure rules just mean that we don't need to worry about the odd
cases as much, because we can just let them be.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Fix nickname saving in XML file to deal with utf8 characters

This makes the whole code much cleaner and simpler.

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