Node ordering for calcnodes

[jehicken]

There are two calcnodes routines, one in the SymCubatures module and one in SummationByParts. This is

1. confusing and
2. dangerous, because the two have different default orderings for the nodes.

Propose to make SummationByParts.calcnodes a front-end for SymCubatures.calcnodes, in which the native ordering in the sbp operator is used.