Use elementwise size in node vertex consistency check (#316)

* use elementwise size in node vertex consistency check

* add comment explaining maximum(..., 1)

* use test based on maximum absolute vertex coordinate instead of element size, and add tests

* assume absolute and relative tolerances are the same for now

* add test for false negatives

* zero-size -> zero-D

* improve vertex consistency check error message

* use a specific exception type for consistency check

* improve tests

* just use relative tolerance and skip dim==0 case

* only do consistency check in debug run

* Reenable 0D tests, remove 1e-5 crit tol scaling, take into account abs tol in node-vert-consistency test tests

Co-authored-by: Andreas Kloeckner <inform@tiker.net>