Redirects for new documentation structure

A meta issue for tackling the documentation restructure https://gitlab.com/gitlab-org/gitlab-ce/issues/3349.

We are moving the worst misplaced items and keeping the old files around with a reference to the new location. For docs.gitlab.com it would be nice to have a 301 redirect in order to train the browsers about the new locations.

• /logs/logs.html to administration/logs.html - https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4622
• /ci/api/ to /api/ci/ - https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4567