Add missing 'get_number_of_citations' method (#859)

* Add missing 'get_number_of_citations' method

* update db test for bsddb

* fix trailing whitespace

* typo

gramps/gen/db/dummydb.py

@@ -32,7 +32,7 @@ database to fetch data from). Thus, dbstate.db cannot be left as 'None' because
 None has no 'is_open' attribute. Therefore this database class is provided so
 that it can be instantiated for dbstate.db.
 
-FIXME: Ideally, only is_open() needs to be implemented here, bacause that is the
+FIXME: Ideally, only is_open() needs to be implemented here, because that is the
 only method that should really be called, but the Gramps code is not perfect,
 and many other methods are called. Calls of other methods could be considered
 bugs, so when these are fixed, this class could be reduced.
@@ -757,6 +757,14 @@ class DummyDb(M_A_M_B("NewBaseClass", (DbReadBase, Callback, object,), {})):
             LOG.warning("database is closed")
         return 0
 
+    def get_number_of_citations(self):
+        """
+        Return the number of citations currently in the database.
+        """
+        if not self.db_is_open:
+            LOG.warning("database is closed")
+        return 0
+
     def get_number_of_tags(self):
         """
         Return the number of tags currently in the database.

gramps/plugins/db/bsddb/test/db_test.py

@@ -81,6 +81,7 @@ class DbTest(unittest.TestCase):
         "get_number_of_places",
         "get_number_of_repositories",
         "get_number_of_sources",
+        "get_number_of_citations",
         "get_number_of_tags",
         "get_media_from_gramps_id",
         "get_media_from_handle",