mobile: fix crash on delete dive from divelist

This is a somewhat hacky commit. For a very long time, the delete
from the divelist on mobile crashed. That is, not always for anyone,
but for me almost consistently. This commit tries to solve it.

I found that trying to save the delete immediately after removing
data from the underlying model seemed to cause the crash. Hacking
around, I found that a simple beginResetModel/endResetModel between
the delete of the underlying model data and actual save is
sufficient to solve the crash.

The big question is, why does this all work? I suspect some of race
condition between deleting model data, and giving the QML engine
the opportunity to do its thing.

This is also related to issue #311, but that is not implemented
here.

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

qt-models/divelistmodel.h

@@ -46,6 +46,7 @@ public:
 	QVariant data(const QModelIndex &index, int role = Qt::DisplayRole) const;
 	QHash<int, QByteArray> roleNames() const;
 	QString startAddDive();
+	void resetInternalData();
 	Q_INVOKABLE DiveObjectHelper* at(int i);
 private:
 	QList<DiveObjectHelper*> m_dives;