[UX Demo] Mockup of Koding integration

We need a prototype branch (aka visiontype) to show how we envision integrating Koding with GitLab so a developer can start with an idea and create code to realize that idea.

Potential Scope

• Buttons for editing via Koding IDE
• Buttons for viewing MR running on Koding
• Integrate Koding into GitLab UI

Links

• Part of https://gitlab.com/gitlab-org/gitlab-ce/issues/19793
• Real issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/12759
• MR for Koding integration: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4769