Bugfix scan_archive and new_jobs

* Refactored new_jobs procedure, more robust way of defining the jobs to do
* Bugfix in new_jobs: for some reason, dates were not properly compared in the database_tools
* Because of the previous: rewrite of a small part of data_availability plot was needed
* added a get_tech method to database_tools to check the type of DB used
* thanks to the previous: force usage of only 1 process in scan_archive if using SQLite
* some minor PEP8 and style related errors