Dive list: implement proper Qt-model semantics for DiveTripModel

Previously, each dive-list modifying function would lead to a
full model reset. Instead, implement proper Qt-model semantics
using beginInsertRows()/endInsertRows(), beginRemoveRows()/
endRemoveRows(), dataChange().

To do so, a DiveListNotifer singleton is generatated, which
broadcasts all changes to the dive-list. Signals are sent by
the commands and received by the DiveTripModel. Signals are
batched by dive-trip. This seems to be an adequate compromise
for the two kinds of list-views (tree and list). In the common
usecase mostly dives of a single trip are affected.

Thus, batching of dives is performed in two positions:
- At command-level to batch by trip
- In DiveTripModel to feed batches of contiguous elements
  to Qt's begin*/end*-functions.

This is conceptually simple, but rather complex code. To avoid
repetition of complex loops, the batching is implemented in
templated-functions, which are passed lambda-functions, which
are called for each batch.

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

core/subsurface-qt/DiveListNotifier.h

@@ -0,0 +1,39 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// The DiveListNotifier emits signals when the dive-list changes (dives/trips created/deleted/moved)
+// Note that vectors are passed by reference, so this will only work for signals inside the UI thread!
+
+#ifndef DIVELISTNOTIFIER_H
+#define DIVELISTNOTIFIER_H
+
+#include "core/dive.h"
+
+#include <QObject>
+
+class DiveListNotifier : public QObject {
+	Q_OBJECT
+signals:
+
+	// Note that there are no signals for trips being added / created / time-shifted,
+	// because these events never happen without a dive being added / created / time-shifted.
+
+	// We send one divesAdded, divesDeleted, divesChanged and divesTimeChanged signal per trip
+	// (non-associated dives being considered part of the null trip). This is ideal for the
+	// tree-view, but might be not-so-perfect for the list view, if trips intermingle or
+	// the deletion spans multiple trips. But most of the time only dives of a single trip
+	// will be affected and trips don't overlap, so these considerations are moot.
+	// Notes:
+	// - The dives are always sorted by start-time.
+	// - The "trip" arguments are null for top-level-dives.
+	void divesAdded(dive_trip *trip, bool addTrip, const QVector<dive *> &dives);
+	void divesDeleted(dive_trip *trip, bool deleteTrip, const QVector<dive *> &dives);
+	void divesChanged(dive_trip *trip, const QVector<dive *> &dives);
+	void divesMovedBetweenTrips(dive_trip *from, dive_trip *to, bool deleteFrom, bool createTo, const QVector<dive *> &dives);
+	void divesTimeChanged(dive_trip *trip, timestamp_t delta, const QVector<dive *> &dives);
+};
+
+// The DiveListNotifier class has no state and no constructor.
+// We can simply define it as a global object.
+extern DiveListNotifier diveListNotifier;
+
+#endif