[MERGE] Add get_username() call to the UIFactory.

[Gary van der Merwe]

bb:coment

+    def get_username(self, prompt, **kwargs):
+        """Prompt the user for a password.

Should that not be :

+    def get_username(self, prompt, **kwargs):
+        """Prompt the user for a user name.


Typical, GUI's will ask for a user name and password with one dialog
box. I'm not sure how one would implement that with this api. I guess
that you could show a dialog that asks for a user name and password
when get_username is called, store the password, and return that
password when get_password is called. But how would you safely match
get_username and get_password calls. It would be much easier if you
had a method for both user name and password. E.g.:

+    def get_username_password(self, prompt, **kwargs):
+        """Prompt the user for a username and password.
...
+        :return:(username, password), return None if the user
+                 canceled the request.

Gary