WIP: Docs api merge 1 ravlen

This is a copy MR of https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/28464, so that we can get the review app working.

• http://review-docs-docs-k4ouxi.178.62.207.141.xip.io/ce/api/group_boards.html
• http://review-docs-docs-k4ouxi.178.62.207.141.xip.io/ce/api/projects.html
• http://review-docs-docs-k4ouxi.178.62.207.141.xip.io/ce/api/protected_branches.html
• http://review-docs-docs-k4ouxi.178.62.207.141.xip.io/ce/api/groups.html
• http://review-docs-docs-k4ouxi.178.62.207.141.xip.io/ce/api/settings.html
• http://review-docs-docs-k4ouxi.178.62.207.141.xip.io/ce/api/merge_requests.html
• http://review-docs-docs-k4ouxi.178.62.207.141.xip.io/ce/api/issues.html
• http://review-docs-docs-k4ouxi.178.62.207.141.xip.io/ce/api/group_milestones.html
• http://review-docs-docs-k4ouxi.178.62.207.141.xip.io/ce/api/milestones.html
• http://review-docs-docs-k4ouxi.178.62.207.141.xip.io/ce/api/users.html
• http://review-docs-docs-k4ouxi.178.62.207.141.xip.io/ce/api/notification_settings.html
• http://review-docs-docs-k4ouxi.178.62.207.141.xip.io/ce/api/namespaces.html