Formalize schema for ostructs.hpp.j2 and onljs.hpp.j2

[brettviren]

The bulk of info given to these templates is in the form of the schema array but there are other attributes of the main object. Right now, Jinja parsing will indicate if a bogus model is given but we want to also be able to validate the model using moo validate.

And for that, of course we need a schema to be developed which embodies the contract with the template.