selectOptionsForFacet View Helper: allow sort prefixes on the strings

and strip them before displaying
allow use of sort prefixes in Autocomplete Facet and Facet Select form item
germania-sacra: use sort prefix for band facet

to go together with indexing from
https://github.com/subugoe/germania-sacra-daten/commit/f48740ac20c875189b47b76e3bff1cb44362f6dc