Referenceprefix manager: Reworked tests and use ftw.testbrowser.
Referenceprefix manager: Removed wrong space in unlock link.
Referenceprefix manager: Fixed KeyError when repository is already removed.
Merge pull request #527 from 4teamwork/pg_referenceprefix_manager_fix

Referenceprefix manager fix, when subitems are already removed.
Add opengever.maintenance to development buildout.
Merge pull request #529 from 4teamwork/lg-add-og-maintenance-to-dev-buildout

Add opengever.maintenance to development buildout.
Include newest theme adjustments for the next release.

Include the fix https://github.com/4teamwork/plonetheme.teamraum/pull/251 which solves #543.
Merge pull request #544 from 4teamwork/pg_icon_for_detailed_view

Include newest theme adjustments for the next release.
Cherrypick from opengever.core release 4.0.

Use correct content-type when returning 'OK' responses.

Conflicts:
	opengever/base/utils.py
	opengever/task/browser/accept/utils.py
Updated the changelog.