SPDX merge for Project

[bs-jokri]

Sometimes one needs to deliver one spdx report for the complete set of dependencies of a project. Since we have spdx reports for all used releases it would be good to directly merge them into one spdx report. Result is one spdx report for all referenced releases of a project.

The spdx-tools should already have a feature that allows to merge spdx reports

for this feature only clearing reports in spdx format are considered