improve OAuth Source Setup process, fix login template, closes #3

passbook/core/models.py

@@ -155,10 +155,15 @@ class Source(PolicyModel):
         return False
 
     @property
-    def get_url(self):
-        """Return URL used for logging in"""
+    def get_login_button(self):
+        """Return a tuple of URL, Icon name and Name"""
         raise NotImplementedError
 
+    @property
+    def additional_info(self):
+        """Return additional Info, such as a callback URL. Show in the administration interface."""
+        return None
+
     def __str__(self):
         return self.name