Standardize token argument in routes.

- `token` becomes `portfolio_token` in routes.
- Find relevant portfolio from token in `before_request` hook, like
  other routes.

templates/emails/portfolio/invitation.txt

@@ -5,6 +5,6 @@
 Join this JEDI Cloud Portfolio
 {{ owner }} has invited you to join a JEDI Cloud Portfolio.  Login now to view or use your JEDI Cloud resources.
 
-{{ url_for("portfolios.accept_invitation", token=token, _external=True) }}
+{{ url_for("portfolios.accept_invitation", portfolio_token=token, _external=True) }}
 
 {% endblock %}