[plugin] New plugin foreman_parameters_summary

Hi all!

I'm please to announce my (first) new plug-in for foreman:
This plug-in adds a new sub-menu "parameter" under "monitor".
This menu will show all common parameters. Select one particular parameter
will show all overridden values.

See https://github.com/david-barbion/foreman_parameters_summary for source
code. The gem is built as well.