Preserve order of box IDs when substituting

[epatters]

After a substituting a box with a wiring diagram (via substitute!), the new IDs of the boxes in the original diagram are undefined. In practice, they are determined by an implementation detail of LightGraphs. Instead, the order of the boxes should be preserved, meaning that if box i is replaced with a diagram with k boxes, the new boxes should have IDs i, ..., i+k-1.

This can be achieved in various ways, but ideally there would be some support for it in LightGraphs (see sbromberger/LightGraphs.jl#1246) and MetaGraphs.

[epatters]

For future reference, the current recommended approach in LightGraphs is described here.