Add facet for subjects, cache all labels parmanently (#81)
Always HTML escape labels retrieved from our API (#81)

The labels often contain a specialization in pointy brackets
(like `Westfalen <Südost>`) which need to be preserved in HTML.
Tweak various labels and texts (main page, navigation, facets)

See https://wiki1.hbz-nrw.de/x/BgCHAg
Update datamaps and add meta tag to fix mouseout issue in IE

See:
https://wiki1.hbz-nrw.de/x/BgCHAg
https://github.com/markmarkoh/datamaps/issues/19