Re-adds a function which was accidently removed.

Commit c1dc7b6b27d4d1c0b45b8f287aa0dc8e90414e77 removed a function which
added the ability to sort a marker selection table.

Fixes https://jira.thehyve.nl/browse/UAT-184
Merge pull request #60 from thehyve/issues/UAT-184-enable-sorting-again

Enable sorting of Marker Selection table again