Allow configuration of files to be scanned for CLI module

After talks at ApacheCon 2019 in Berlin higryspotiuk asked for a possibility to specify the files that need to be scanned.

This could be added as a new CLI option that specifies a file to read from.
Each line will contain one file that RAT scans with its default configuration (as the current CLI scan does).

Thus a possible run would be:

java -jar rat.jar -scan myfiles.txt

"-scan" will be an exclusive option, thus all other existing
exclusions options will not be allowed, when this option is used.

myfile.txt may contain comments (starting with "#") or empty lines, all else will be treated as files.