v2.4 - Command lines (linux) & Relative paths improvement

Main improvements:
- CATALOGS & COMMAND LINE: it is now possible to use 3 actions from command line: list_catalogs, update_catalogs, and update_all_active. Get the details by typing ./Katalog --help from the application executable location.
- SETTINGS: It is possible to use relative path for the Collection folder or the Database file path, making Katalog more portable. The handling of the input has been improved.

Full list of updates:
https://github.com/StephaneCouturier/Katalog/issues?q=milestone%3A2.3+sort%3Acreated-asc

Full code changelog:
https://github.com/StephaneCouturier/Katalog/compare/v2.3...v2.4

Download Katalog:
https://sourceforge.net/projects/katalogg

Documentation
https://stephanecouturier.github.io/Katalog