mobile cleanup: unduplicate code and do not loop over dives (1)

This is the first of a set of commits that are (very) similar.
It appeared that a number of more or less static lists, which are
constructed by a loop over all dives in the logbook, were executed
when changing focus to a next dive. For example, the in this
commit addressed list of used dive suits.

What was wrong was that the suitList was linked to a dive. There
is only a need to construct the list of used suits when data is
changed (and obviously, once on startup of the app). Further, it
appeared that a lot of code was duplicated and that we can use
(in this case) the same code from the desktop completionmodels.cpp.

Basically, this commit involves the following changes:
- include completionmodels.cpp in mobile and desktop (so move
it from the desktop only category to the generic category).
- remove double code from DiveObjectHelper.cpp
- Do not differentiate in the init phase and the normal refresh
of the list
- the per dive logic is now only the getting of a previously
constructed list (in init or update of the divelist).

There are no visible changes in the UI, other than a better
performance when scrolling over dive details.

Signed-off-by: Jan Mulder <jlmulder@xs4all.nl>

core/subsurface-qt/DiveObjectHelper.cpp

@@ -411,21 +411,6 @@ QString DiveObjectHelper::firstGas() const
 	return gas;
 }
 
-QStringList DiveObjectHelper::suitList() const
-{
-	QStringList suits;
-	struct dive *d;
-	int i = 0;
-	for_each_dive (i, d) {
-		QString temp = d->suit;
-		if (!temp.isEmpty())
-			suits << d->suit;
-	}
-	suits.removeDuplicates();
-	suits.sort();
-	return suits;
-}
-
 QStringList DiveObjectHelper::locationList() const
 {
 	QStringList locations;