arccore.graph weighted edge traverse enhancement

[ChrisRus]

I just release v0.1.9 crescent with support for weigted edge BFT/DFT.

In hindsight I missed an rather obvious usability enhanancement.

Currently, to enable edge-weighted traversal you need to add getEdgeWeight and compareEdgeWeights callback function definitions to your visitor object.

But, in the vast majority of cases the developer-defined edge weight will a value of a type that is comparable via standard less-than and greater-than operators (e.g. string, numeric value).

So, we should allow developers to specify on getEdgeWeight to enable edge-weight traversal feature. And, allow compareEdgeWeight to be left unspecified in order to use default comparison operator provided by graph library (should be sufficient for 80% of use cases).