Refactor and simplify RingdownStatus

[fwextensions]

• Add StatusList and StatusStep to simplify markup
• Add is() to DeliveryStatus to check the current ringdown status matches a target status.
• Add StatusButton and Timestamp components to RingdownStatus.js.
• Destructure local vars from ringdown to reduce code.
• Add StatusList.js and Timestamp.js.
• Move status list styles to StatusList.scss.
• Update timestamps to consistently use AM/PM.

The simple StatusButton component in RingdownStatus doesn't have propTypes, since it's only used in that file, but that could be added if desired.