new ViewHelper: ValueForKey

to read _variable_ items out of arrays

supports JSON output (optional)
use ValueForKey View Helper in Result Partial
Improve templating for Facets

* separate partial for facet item
* logic to only show a limited number of facets by default
	* includes TypoScript configuration for a default which can be overriden per field
	* includes JavaScript to un-hide the additional facets later on
clean up Index template
linked / overridden templates / partials for germania-sacra testing