Providing better feedback on checking for libraries

[Removed by request]

I'm using Pipelight 0.2.8.2 and on executing "pipelight-plugin --system-check" if a library is missing it is shown as "missing" and the final output for the libraries shows "Libraries: FAILURE". Maybe this can be enhanced to make a difference between missing dependencies and missing recommended packages. For example instead of showing "missing" for the related library it could be additionally hinted if this library is required or optional. And the last line could for example show something like "Libraries: SEMI-PASSED" if only optional libraries are missing.