Improve JavaScript components docs

[Archmonger]

Current Situation

The current docs are sparse on information, making it hard for new users to develop custom components. In particular, we jump to a relatively complicated example with super-simple-chart without ever showing a "Hello World" example. Also, this example does not demonstrate interactivity.

Proposed Actions

Extend the docs to add the following information

• Simple "Hello World"
• Adding interactivity (event handling)
• Sending arbitrary JS data to Python
• Sending arbitrary Python data to JS
• Using a ReactJS component in a custom component