Updated language file to match 1.x trunk.
Initial Sierra driver courtesy of Julia Bauder.
Added missing comment.
Resolving VUFIND-770 (string "0" is not translated).
Condition for ignoring rows of translation file was too general.
Thanks to Josef Moravec for the fix.
Use URL helper to generate query parameters instead of manual method.
New method BackendInterface method: Return backend identifier

* VuFindSearch/Backend/BackendInterface.php (getIdentifier): New
  method. Return backend identifier.
Added JSON update handler for RecordManager compatibility.
Implemented highlighting.
Moved MultiIndexListener to different namespace.
Fixed failing tests by adding missing service.
Merge branch 'master' into search-refactor