more test coverage
more tests for the generic sparql class
added limit and offset for alphabetical index search functions also added a few unit tests for these
initial implementation of REST search fields parameter (issue #22), still buggy (e.g. returns multiple types, lacking escaping of backslashes in labels, problems with missing labels)
REST fields parameter: don't break if broader concepts are missing labels
Merge branch 'rest-fields-issue-22' of https://github.com/NatLibFi/Skosmos into rest-fields-issue-22