Make top-level control groupings collapsible

## Use Case

Part of UI consistency overhaul

## Solution

As a reusable component we want a top-level collapsible widget that can be a container for a set of controls or a layout. TBD: under what conditions should content inside the widget scroll instead of expanding fully? Do we still require docking?
Can we just take the Section widget and make it both dockable, and contain sub-sections?

## Alternatives

_Please describe any alternatives you've considered, even if you've dismissed them_