Avoided overwriting of files

[TwoOfTwelve]

Avoids overwriting of existing results files. Tries to find a new unique filename by adding (). Aborts if the selected file is not writable. Also adds a cli option --overwrite, that ignores existing files. This still aborts if the file cannot be written.

Solved #1670

[tsaglam]

@TwoOfTwelve could you add a small test for this?

[sonarcloud[bot]]

Quality Gate passed for 'JPlag Plagiarism Detector'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
88.6% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud