DATASOLR-162 - Allow pagination using cursorMark.

We introduced Cursor<T> and its implementation DelegatingCursor<T> to allow deep pagination using CursorMarkParams.CURSOR_MARK_PARAM.

This allows simple iteration over query results only fetching those documents at given cursorMark. The number of documents returned is controlled by the Pageable provided by the Query itself. Use SolrTemplate.queryForCursor when you want to do deep pagination.

Please note that using cursors is only possible in case any sorting parameter is applied to the query.