Dev fix: The sort classes were being applied regardless of `sort` and
`sortClasses`
Dev fix: _pluck should check that what is is accessing exists

- When using _pluck with deferred rendering, there were a number of
  errors due to the nTr element being undefined (that's what deferred
  rendering is all about of course). So the logic to check that pluck
  can pluck from a source object needs ot be added.
Dev fix: Call number formatter in the correct scope