Set a URI on Auth Messages, so the "Change Details" dialog from the transaction record has a cancel button
If you edit an auth message in Auth > Customize Messages, then click "Show Details" in the transaction record, the resulting dialog uses the object's handle's URI to generate a "cancel" button.
Since these handles currently have no URI, the dialog currently has no cancel/done button to close it.
Test Plan: Edited an auth message, clicked "Show Details", was now able to click "Done" to close the dialog.
Reviewed By: amckinley
Differential Revision: https://secure.phabricator.com/D20471