Move SAST parsing and data storage to CE

Problem to solve

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

This task requires that all the parsing and the data storage are available in the gitlab-ce codebase.

Further details

This is independent from the data visualization (e.g., security reports in the MR widget).

Proposal

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