HTML output with RDFa

Output index content (lobid resources, organisations, and GND entries) as HTML with RDFa.

The resulting HTML is modeled after the current output at lobid.org. It is implemented using Play templates. There is one template tag ('rdfa') that contains the reusable HTML blocks: [rdfa.scala.html](https://github.com/fsteeg/lodmill/blob/72feca175dcbaad3ed6e5cf24044b3b5fd4bad6b/lodmill-ui/app/views/tags/rdfa.scala.html).

By using this 'rdfa' tag, the actual templates for resources, organisations, and GND entries become quite concise: [resource.scala.html](https://github.com/fsteeg/lodmill/blob/72feca175dcbaad3ed6e5cf24044b3b5fd4bad6b/lodmill-ui/app/views/tags/resource.scala.html), [organisation.scala.html](https://github.com/fsteeg/lodmill/blob/72feca175dcbaad3ed6e5cf24044b3b5fd4bad6b/lodmill-ui/app/views/tags/organisation.scala.html), [gnd.scala.html](https://github.com/fsteeg/lodmill/blob/72feca175dcbaad3ed6e5cf24044b3b5fd4bad6b/lodmill-ui/app/views/tags/gnd.scala.html).

See example output for [resources](http://api.lobid.org/id/HT002189125?format=page), [organisations](http://api.lobid.org/search?format=page&index=lobid-orgs-index&category=title&query=Technische+Universit%C3%A4t+Graz), and [GND entries](http://api.lobid.org/search?format=page&index=gnd-index&category=author&query=Schmidt%2C+Hannelore+%281919-2010%29) (on http://api.lobid.org).