cleanup: invert control-flow when resetting the core structures

To reset the core data structures, the mobile and desktop UIs
were calling into the dive-list models, which then reset the
core data structures, themselves and the unrelated
locationinformation model. The UI code then reset various other
things, such as the TankInformation model or the map. . This was
unsatisfying from a control-flow perspective, as the models should
display the core data, not act on it. Moreover, this meant lots
of intricate intermodule-dependencies.

Thus, straighten up the control flow: give the C core the
possibility to send a "all data reset" event. And do that
in those functions that reset the core data structures.
Let each module react to this event by itself. This removes
inter-module dependencies. For example, the MainWindow now
doesn't have to reset the TankInfoModel or the MapWidget.

Then, to reset the core data structures, let the UI code
simply directly call the respective core functions.

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

qt-models/divetripmodel.h

@@ -64,12 +64,6 @@ public:
 	// Call after having set the model to be informed of the current selection.
 	void initSelection();
 
-	// Clear all dives
-	void clear();
-
-	// Reload data
-	void reset();
-
 	Qt::ItemFlags flags(const QModelIndex &index) const;
 	QVariant headerData(int section, Qt::Orientation orientation, int role = Qt::DisplayRole) const override;
 	DiveTripModelBase(QObject *parent = 0);
@@ -78,6 +72,8 @@ public:
 	// Used for sorting. This is a bit of a layering violation, as sorting should be performed
 	// by the higher-up QSortFilterProxyModel, but it makes things so much easier!
 	virtual bool lessThan(const QModelIndex &i1, const QModelIndex &i2) const = 0;
+protected slots:
+	void reset();
 signals:
 	// The propagation of selection changes is complex.
 	// The control flow of dive-selection goes: