Fix: Memory was not being fully released on destroy.
Fix: Memory was not being fully released on destroy.

A number of individual issues:

* The removal of the event handlers did not remove the `touchstart`
  event
* Removal of the event handlers didn't take the wheel event name into
  account
* The header was being deep copied three times with full events for all
  child elements. The result was that elements which were not being
  added to the DOM still had event handlers (click to sort) and
  therefore could not be reached in future to remove them and their
  event handlers. The fix is to deep copy, but only shallow copy the
  events and data, which jQuery's `clone()` method as an option for.
  That way, cells which aren't used can just be GCed.

modulexcite/FixedColumns,modulexcite/FixedColumns,nickzhuyb/FixedColumns,nickzhuyb/FixedColumns