Clearer stratify

[mwdchang]

Summary

This enables fuller MIRA stratify capabilities, and try to use an easier to understand language.

• directed: this is hidden and assume to be true
• structure: this is proxied by useStructure (true | false), where true = None = all combinations and false = [] = nothing

Cartesian =~ Allow existing transitions to involve multiple strata
Structure =~ Create new transitions between strata

Testing

Structure toggle works, you need to have beaker instance running.