#196 Add WES as metric for DCSH variable ordering algorithm

General/preparatory changes:

• VarOrderHelper and HyperEdgeCreator store variables as a list.
• Dynamic metric width, to reduce width and make room for extra metric.
• Renamed dbgTotalSpan* to dbgMetrics*.

Add WES:

• Added WES as variable ordering metric.
• Added more unit tests. (these found several issues while I was working on this issue)
• ChoiceVarOrderer support for arbitrary metrics.
• DCSH uses WES.

Reviewing per commit may be easier than reviewing the full diff.

Addresses #196 (closed)