SPDX Export at software component level from the UI

[pellecchialuigi]

Actually, fro the UI, we can export to SPDX only a complete library.
That means BASIL will iterate over all the software components available in the selected library and will generate a single json file with all the data.
It will be useful to be able, from the UI, to export also a single software component in SPDX Json format.