(PUP-2452) Refresh support for Package type

This is implemented behind a feature that each provider must implement. It is intended to allow source distributions to recompile packages on a notify or subscribe event.

It allows patterns like:

    package { "www-servers/nginx":
       ensure    => latest,
       subscribe => File['/path/to/nginx/compile/options'];
    }
We're leaning toward `reinstallable` as a more consistent name with the other package features than `refreshable`.  Would you be able to update this PR accordingly?


Thanks!