Use a topological sort of variable bindings when building the beta tree

[rbrush]

The sort order for rule constraints is somewhat arbitrary and confusing, as can be seen in the clara.rules.compiler/condition-comp function, and accumulators that use the result bindings of other accumulators in the same rule may yield an error on compilation time.

We can address this by doing a topologic sort on the variable bindings used by conditions. This issue is to evaluate and track that effort.

[rbrush]

Closing! This has been merged into master.