High Order Elements

Interested parties: Berk, Jeremy (and probably others)

Initial implementation (now reverted): add a "order" data member to Field which specifies piecewise constant vs linear, etc. This was not very flexible, so as of 2016/03/02 we are removing it.

Berk's suggestion is that we should specify a set of basis functions, and that this should be part of a 3rd-party library that both VTK and VTK-m can use. This would decouple e.g. the order of the element with its interpolation functions.

Jeremy suspects this might be a way to allow e.g. a point scalar (piecewise linear) field and a cell (piecewise constant) scalar field to be combined into a piecewise quadradatic scalar field.