Add unit tests and integration tests for the candidate network edge set of a given graph

[recursion-ninja]

We need a lot more tests for this!

[recursion-ninja]

Property, if we have a valid network N0 and another valid network N1 then the graph:

   r
 /   \
N0    N1

should have a number of candidate network edges equal to the product of the number of candidate network edges in N0 and the number of candidate network edges of N1 minus the number of network edges.

We can start testing this property with binary trees and explore simple network constructions to arbitrarily generate.

[recursion-ninja]

Property, if we have a valid network N0, N1, N2, and N3 then the graph:

      r
   /     \
 N0       a
         / \
       b     c
     /  \  /  \
    N1   d     N3
         |
        N2

There should be no candidate network edges between (a,b), (a,c), and any edges from N1, N2, or N3.

[recursion-ninja]

Property, if we have a valid networks N0, N1, and N2; then the graph:

      r
    /   \
  N0     x
        / \
       N1  N2

should not have any network edges from (r,x), (x,N1), (x, N2). and any edges in N1 or N2.

[Boarders]

This is now (hopefully!) complete as of this commit: https://github.com/amnh/PCG/commit/2ed85b430d2e6bc02f975954840fb04910f36e01

[recursion-ninja]

This looks absolutely great!