Add language and detail facets for historical agents
Better formatting for list elements
Minor cleanup
Add messages for ISAD(G) level of description
Show emails and urls when rendering addresses (fixes #399)
Improvements to the signup and password-reset pages
Fix display of events title
Retooling of search hit highlighting (fixes #407).

 - Highlighting no longer attempts to munge a whole chunk of Html,
   it now has to be applied individually to fields
 - Added a new interface for a `Highlighter` with a highlight method
   and made `SearchHit` implement this, which allows using a dummy
   highlighter when there's no hit available
 - Still a bit WIP...
Add a custom 500 error view for production. Also rename some i18n keys
Undo a deliberate error used for testing the error page (whoops)
Merge branch 'master' into virtual_collection_rework

Conflicts:
	modules/portal/app/views/p/documentaryUnit/searchItem.scala.html
Merge branch 'virtual_collection_rework' into merge_guides2