Clarify conventions around declaring Class properties vs heritableProperties in the core-im

[mbrush]

Can someone define the rationale for when to use one vs the other was chosen in the current core-im model?

I suspect if has to do with whether the class has subtypes in the core model (but the whole profiling framework adds a twist here).

Once the rules are clear, we should review their current usage, and fix any that need fixing?

[ahwagner]

This is a metaschema processor convention. heritableProperties are used by abstract classes, properties by concrete classes. You'll note that when processed to JSON Schema, there are no data classes that retain a heritableProperties property.

[mbrush]

Thanks Alex - I fixed incorrect usages of heritableProperties in PR #154.