DEL must mesh on entire set

[mdsumner]

Possibly make this an opt-out, or maybe it's a different model?

[mdsumner]

related is that DEL.SC is not normalizing in x/y, so do that first (it is for DEL.PATH causing head scratching here hypertidy/silicate#62 (comment))

( I think the SC methods are wrong somewhere, it doesn't show up because the edges are fine on their own, it's only when related it comes out wrong)

[mdsumner]

Here's a scgraph plot for edges and vertices

library(scgraph)
library(ggraph)
ggraph(as.igraph(x)) + 
geom_edge_link(aes(label = edge_, 
  start_cap = label_rect(node1.name)),  angle_calc = 'along', label_dodge = unit(2.5, 'mm')) +  
 geom_node_text(aes(label = name))

[mdsumner]

DEL.SC now normalizes correctly, and the silicate#62 example now works.

DEL should still work set-wise, it will simplify the code a lot - but it's not clear if we should classify holes set-wise or individually (probably need it to be an option, with post-iterate normalization).

[mdsumner]

We can't do this set-wise without turning SC into PATH. It has to be done