LP#1812389: make Group Penalty Threshold admin page accessible again

LP#1812389: make Group Penalty Threshold admin page accessible again

As a consequence of the patch for bug 1744756 adding a new
admin/local/permission AngularJS app, the routing for
admin/local/permission/grp_penalty_threshold got broken, making the
embdeded Conify interface for group penalty thresholds inaccessible
from the web staff client. This patch fixes that.

To test
-------
[1] From Administration | Local Administration, go to Group Penalty
    Thresholds. Note that the embedded Conify admin interface
    is not displayed and the URL changes to .../permission/grp_tree.
[2] Apply the patch and repeat step 1. This time, the admin interface
    should appear.
[3] Verify that the Permission Group Tree Entries interface remains
    accessible from Local Administration.

Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>