[Fixes #900] Use [Route(...)] on action methods to specify an attribute ...

...route that allows all verbs.

1. Changed attribute usage on RouteAttribute.
2. Added a test on action discovery to ensure that actions with [Route] get discovered as
   attribute routed actions.
3. Added a test on reflected action descriptor provider to ensure that an action with [Route] on
   the controller and [Route] on the action results in an action that allows any Http method.
I've added a comment to explain the intent.