Move Security Reports in the pipelines view to CE

Problem to solve

We are considering to move Security Reports in the pipelines view to gitlab-ce and make it opensource. See discussion in &440 (closed) for more information and timelines.

This task requires that all the frontend and backend is available in the gitlab-ce codebase.

Further details

This is independent from the data parsing and storage, and addressing the pipelines view only.

Proposal

Port relevant code from gitlab-ee to gitlab-ce, removing any license check for it.