Revert "Empty point sets are re-rendered as well"

This reverts commit 588ecb3df3b8782b26ea7af5817961c417e2cae3.
Revert "Sanity check if the point set is empty"

This reverts commit a3efa8e3659363e47b8241a76f39039d119d6c2c.
Deleting last point from visualization
README file updated
Merge branch 'trac-3581-last-point-of-point-set-stays-visible' into niftk-2013.09