core: use std::vector<> to store divecomputer samples

This is a hairy one, because the sample code is rather tricky.

There was a pattern of looping through pairs of adjacent samples,
for interpolation purposes. Add an range adapter to generalize
such loops.

Removes the finish_sample() function: The code would call
prepare_sample() to start parsing of samples and then
finish_sample() to actuall add it. I.e. a kind of commit().

Since, with one exception, all users of prepare_sample()
called finish_sample() in all code paths, we might just add
the sample in the first place. The exception was sample_end()
in parse.cpp. This brings a small change: samples are now
added, even if they could only be parsed partially. I doubt
that this makes any difference, since it will only happen
for broken divelogs anyway.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

profile-widget/profilescene.cpp

@@ -428,7 +428,7 @@ void ProfileScene::plotDive(const struct dive *dIn, int dcIn, DivePlannerPointsM
 	}
 
 	const struct divecomputer *currentdc = get_dive_dc_const(d, dc);
-	if (!currentdc || !currentdc->samples) {
+	if (!currentdc || currentdc->samples.empty()) {
 		clear();
 		return;
 	}