Create a distinction between childFields and innerFields

[bmv437]

Are you submitting a bug report or a feature request?

Idea for a new feature

What is the current behavior?

Currently the generator can't tell the difference between childFields and innerFields.

• Some fields are comprised of multiple innerFields, which is different than the existing parent <-> childFields relationship
• innerFields are part of the current field, while childFields are not.
• A shallow validation should validate innerFields and not childFields
• A deep validation should validate innerFields in addition to childFields
• We currently use the fields prop in combination with _genChildren to talk about innerFields. An example would be the dateUnknown field.

This comes into play with the new mapFieldChildren() function which was introduced in #13
For validation iterators (ex: isSectionValidIterator()) that are executed with deep: false, it will skip innerFields (which is currently achieved with _genChildren).

Should we support innerFields as first class citizens in the generator?