Update for gridview code to improve speedup

The code to select sample_codes from observation_fact has been adjusted
to also select on patient_num. In combination with the newly created index
(see tranSMART-ETL), this speeds up the process significantly.
Removed some unnecessary code from the improvement
Merge pull request #27 from thehyve/issues/UAT-127-grid-view-speedup

Issues/uat 127 grid view speedup