Make all EntityType fields include MapStorage by default.

This is to help developers not have to remember to specify it as a Representation.
Add Calculation as a Representation.

It includes renaming GeneratedField to Calculation to avoid having too many names in the model.
Eliminate debatable todo.
Add Derived fields.
Add Name.toPlural.
Extract QualifiedTypeProvidingFieldName from EntityName to make it more general.
Add CrudPersistence.save(Option[ID], SourceType, source, RequestContext)

It is a convenience method.
Also rename EntityType.idFieldDeclaration to id.
Create external functions for UriPath.

This is in preparation for inlining them to eliminate the UriPath class.
Add EntityNavigation.topLevelActions.