Return to natural order sorting

This change allows a column to be returned to its original state after being sorted. This is very important for some customers who, in certain circumstances, need to preserve the original ordering of table items. Within this pull request is the code for the implementation, a unit test, and documentation. If this is an acceptable change, I can also update the documentation on the Smart-Table website. I would really like to see this feature implemented and would love more feedback on what I could do to get this in there.