Change default behaviour so that all code files are considered

[copernico]

Some projects, such as Ambari, use a variety of languages so it is cumbersome to have to specify which extensions to consider.

The default behaviour could be changed so that any file from a known code extension is considered (we could take a reasonable list of such extensions as a starting point, e.g. java, c, cpp, h, js, jsp, py, go, rb).

example: CVE-2020-1936

Ambari is developed in java + javascript + python (+a few others). The fix commit is easily identified by specifying --filter-languages=js, but it is discarded otherwise.