puppetboard/app.py: Simplifying the Inventory Code (#289)

• puppetboard/app.py: Simplifying the code generating and rendering the Inventory

This resolves #275

This update eliminates one iteration over the resulting inventory facts
that generates a multidimensional dictionary keyed by the node's certname
to another dictionary of key-value pairs of the fact name and fact value.

• puppetboard/templates/inventory.html: Wrapping the fact values in links to the Node page

This comes as a request from #280