Add some password-related feature (#92)

* Add Standalone Password Generator. Closes #18 
* Add an entropy meter for passwords. Closes #84
* Don't require password repeat when it is visible. Fixes #27

tests/gui/TestGui.h

@@ -42,6 +42,7 @@ private Q_SLOTS:
     void testTabs();
     void testEditEntry();
     void testAddEntry();
+    void testEntryEntropy();
     void testSearch();
     void testDeleteEntry();
     void testCloneEntry();