Add custom icons when merging. (#1008)

* Adding missing custom icons on merge.
* qDebug when adding icon
* Adding test for merge custom icons.

tests/TestMerge.h

@@ -38,6 +38,7 @@ private slots:
     void testCreateNewGroups();
     void testUpdateEntryDifferentLocation();
     void testMergeAndSync();
+    void testMergeCustomIcons();
 
 private:
     Database* createTestDatabase();