Strip whitespace from username field when editing User

Otherwise can be a gotcha, if user doesn't know their username "has a
space" etc.

tailbone/views/users.py

@@ -157,7 +157,7 @@ class UsersView(MasterView):
             readonly=True)
 
     def configure_fieldset(self, fs):
-        fs.username.set(validate=unique_username)
+        fs.username.set(renderer=forms.renderers.StrippedTextFieldRenderer, validate=unique_username)
         fs.person.set(options=[])
         fs.person.set(renderer=forms.renderers.PersonFieldLinkRenderer)
         fs.append(PasswordField('password', label="Set Password"))