Replace gunicorn with wsgiref

The patch replaces gunicorn with wsgiref since it doesn't make sense to
have gunicorn as dependency. Lets let deployers choose whatever the
prefer to use as container.

The patch also removes lib/* since marconi_paste is not needed anymore,
the wsgi app can now be accessed through:

    `marconi.transport.wsgi.app:app`

Backward incompatible change: bind refers now to the host and a new
config variable was introduced to specify the port it should bind to.

Fixes bug: #1187280
Implements blueprint: transport-wsgi

Change-Id: I9f7767ace5c6553e75e2f4587032d7d64b9537c4
Merge "Replace gunicorn with wsgiref"