Add --exit-code option

[pnu-s]

Add an option exit-code to allow the script user to change the returned exit code in case of trackers found.

Could be used for instance to run with --exit-code 0 to avoid failing or --exit-code 1 to avoid the current exit codes (based on the number of found trackers).

[DMyachin]

https://github.com/Exodus-Privacy/exodus-standalone/pull/44/files