Re-evaluate distinction between presentational and composite components

[lyzadanger]

The package currently distinguishes between presentational and composite components. To some extent this distinction makes sense — composite components are composed of numerous components, and by design don't allow as much control over their constituent component's configurations or styling — but I'm not (entirely) convinced anymore that the distinction need be made at an API level.

There's some blurring of the line between presentational and composite. Dialog, for example, is structured like a composite component but accepts presentational props (specifically, it allows classes, which the composite-component API does not).

I'd like to review the division at some point to see if it still makes sense as it is presently expressed. Having fewer types of components versus more is better for consumers and stability.

[lyzadanger]

Notes:

• Dialog and ModalDialog claim to be composite components in docs but are implemented as presentational components
• Is the classes prop more accurately part of the styling API?