Add licensecheck related command

[sanjayankur31]

A common task we package maintainers need to carry out when updating bits to new releases (or even packaging new stuff) is to run a licensecheck on the package sources. I often end up at least untarring the sources and running licensecheck -r .. | sed '/UNKNOWN/d' to get a summary at least.

Would something like this be useful to add to fbrnch (perhaps with more intelligence to try to detect bundled bits and so on)?