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>

mobile-widgets/qml/DiveDetailsEdit.qml

@@ -224,8 +224,7 @@ Item {
 			}
 			HintsTextEdit {
 				id: suitBox
-				model: diveDetailsListView.currentItem && diveDetailsListView.currentItem.modelData !== null ?
-					diveDetailsListView.currentItem.modelData.dive.suitList : null
+				model: manager.suitList
 				inputMethodHints: Qt.ImhNoPredictiveText
 				Layout.fillWidth: true
 			}