feat(wsgi): message bulk deletion

The purpose of this feature is to allow the "Location" header
returned from message posting to accept the DELETE method.

    DELETE /queues/q/messages?ids=msgid1,msgid2...

Note that if the "ids" parameter is not present, such an
operation will be denied.

Change-Id: Id8313a675c2427b772f1e9095452dda4d0d67432
Implements: blueprint message-bulk-delete
Fixes: bug #1201649
Merge "feat(wsgi): message bulk deletion"