Read interaction feed URI and query support with API.

If a server provides an interaction feed then it is read. Interaction support
can be queried (true/false) from the API.

This information is output in the server info script.
Add ratom and launchy gems to the runtime dependencies.

We will use ratom for parsing the interaction feed. Launchy will be used in the
run-workflow script to open interactions in a browser.
Read notifications from the interaction feed.

A method is provided in the Run class to read new notifications. The
run-workflow script will open notifications in a Web browser if it can.
Document the Interaction Service additions in the README.