Compare synthesis reports with previous builds

Created by: vloncar

Adds script (compare-reports.sh) that compares reports generated from previous stage (gather-reports.sh). On Jenkins side, this will work by saving the report as the build "artifact", and then use the artifact of last successful build of master branch as the baseline for comparison. Not yet complete, currently only records artifacts. The comparison part will be added once I see how the artifacts are exposed through Jenkins API.