Message support in SQlite.

 * The JSON serialization is switched to msgpack;
 * list() on messages and stats() on queues fail loudly.

Implements: blueprint message-pagination

Change-Id: Iadb1ef348a53e0de28c6b45782ef686a3f1bf1e2
Message support in WSGI.

Implements: blueprint transport-wsgi

Change-Id: I8c3908ce7e74da26b3ebebd06f308754665d681b