PYCBC-68, PYCBC-64, PYCBC-8: Design Doc Management

This changeset introduces the design_* set of methods for deleting,
creating, publishing and inspecting design documents.

- The c._design method has been removed as well. c.design_create()
  should be used instead

Change-Id: I44193908a31395b892e8c026db294eef5e313553
Reviewed-on: http://review.couchbase.org/26727
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Mordechai Nunberg <mnunberg@haskalah.org>