Add runners API

References #4264

See merge request !2640

Put project visibility icon next to title

Fixes #11872

See merge request !2885

iChange `name` and `path` to `name_with_namespace` and `path_with_namespace` in `RunnerProjectDetails`

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- add feature to list runners
- add feature to show runners details
- add feature to delete runner
- add feature to update runner

Update web editor documentation

Based on https://gitlab.com/gitlab-com/www-gitlab-com/merge_requests/1045

Closes #4262

See merge request !2776

Project limit is reached warning is hidden when the projects_limit is zero

Fixes #12791

See merge request !2890