Fixes #8379 : Add plugin knowledge to foreman_hooks.

This includes two changes.
1) Strip the module name off of the class, so that Katello::Product looks like Product
2) Append a plugins asset paths to the Rabl view_paths

The second option uses a new plugin.path attribute if it is available. The path was added
by #8325. The plugin assumes an engine layout which is apps/views and app/views/$PLUGIN

The README is also updated to note this works with plugins.