spdxalien: add option to skip import of scancode findings

We are switching to Fossology 4.1.0, which has a new agent/plugin that launches and imports scancode findings and displays them in a more effective way in Fossology GUI (currently scancode findings and debian findings are imported through the ReportImport agent, and it's hard to understand from the GUI which finding comes from scancode and which one from debian).

Therefore, import of scancode findings through spdxalien command (which creates the spdx file to be imported via ReportImport) should be made optional