BugFix - Improvement of scan_archive and new_jobs

Thanks to some great early MSNoise adopters who reported problems using the mailing-list, we have identified a few bugs and tricky situations where some steps failed. This is the case for

• scan_archive: there were major issues using Threads, this step uses Process for multiprocessing, which is much safer. The only problem remaining is that there is no more console-logging of the found/identified files. To be corrected soon.
• new_jobs: mostly rewritten, all jobs are properly identified now. There should no more lost jobs !

I've also reflected those changes in the documentation.