Improve existing code prior to implementing FDO Secrets

* DatabaseTabWidget::newDatabase returns the created DatabaseWidget
* Emit DatabaseTabWidget::databaseOpened signal before a new tab is added
* EntrySearcher can now search attribute values including custom ones
* Add Group::applyGroupIconTo to set the group icon on the supplied entry
* Implement desktop notifications through the system tray icon
* Add DatabaseWidget::deleteEntries to delete a list of entries
* Add Aes128 in SymmetricCipher::algorithmIvSize
* Add DatabaseWidget::databaseReplaced signal
* Add a helper class to override the message box's parent (prevent bugs)

tests/TestEntrySearcher.h

@@ -35,6 +35,7 @@ private slots:
     void testSearch();
     void testAllAttributesAreSearched();
     void testSearchTermParser();
+    void testCustomAttributesAreSearched();
 
 private:
     Group* m_rootGroup;