Add more details about the FormView object

[weaverryan]

I think in some cases, users will need to short-circuit the normal rendering and use values on the FormView object directly. We should have a quick note about the common things available on this object - such as the label and the id - and how to use them.

[weaverryan]

This has been partially accomplished. However, I'd like to see an example of using buildView and buildViewBottomUp in the form_customizations entry. For example, simply adding a variable to one of the field's View object and rendering it in the template is a great example.

[weaverryan]

This may be covered now. To be sure, we may need a newcomer to look at the form docs and try to figure out what all the buildView and form variables do :). I'm going to close this now - since these docs are quite important, we'll likely re-read them sometime soon to make sure we're covered well. The point is, at the very least, this is all documented in the create_custom_field_type.rst document.