Bump content_models and exclude campaigns from Rummager

Cherry picked from upstream: a0e4247e
Add "Save and continue editing" to new artefact form
Add support for help page artefacts.

Cherry picked from upstream and modified to not explode as odi does not use help pages.
Merge pull request #69 from theodi/gds_upgrade_add_help_pages

Gds upgrade add help pages