Undo: keep frontend informed of changes to dive site count

Add a new signal to DiveListNotifier. Send signal if dives are
added or removed and therefore the dive count of a dive site
changes. The dive sites are collected and the signal is sent
at the end of the command.

Add code to update the table view.

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

core/divesite.c

@@ -23,6 +23,7 @@ int get_divesite_idx(const struct dive_site *ds, struct dive_site_table *ds_tabl
 	return -1;
 }
 
+// TODO: keep table sorted by UUID and do a binary search?
 struct dive_site *get_dive_site_by_uuid(uint32_t uuid, struct dive_site_table *ds_table)
 {
 	int i;

core/subsurface-qt/DiveListNotifier.h

@@ -42,6 +42,9 @@ signals:
 	void divesDeselected(dive_trip *trip, const QVector<dive *> &dives);
 	void currentDiveChanged();
 	void selectionChanged();
+
+	// Dive site signals
+	void diveSiteDiveCountChanged(dive_site *ds);
 public:
 	// Desktop uses the QTreeView class to present the list of dives. The layout
 	// of this class gives us a very fundamental problem, as we can not easily