Create "Managing State" Document

[rmorshea]

Current Situation

The docs are still unfinished. The next major set of sections to complete is "Managing State"

Proposed Actions

Write the "Managing State" documentation as per the React docs: https://beta.reactjs.org/learn/managing-state

Work Items

Write the following sections.

• Managing State
  • Reacting to Input with State
  • Choosing the State Structure
  • Sharing State Between Components
  • Preserving and Resetting State
  • Extracting State Logic into a Reducer
  • Passing Data Deeply with Context
  • Scaling Up with Reducer and Context

[Archmonger]

Closing this in favor of the docs rewrite #863