Add: dynamically load JavaScript for each component.

[bjones1]

This PR makes all Runestone Components dynamically loaded. The basic approach:

• When the document is ready, search for all HTML entities with a data-component attribute (which only occurs for the Runestone components). Use the value of this attribute (which is the name of the Runestone component) to dynamically load code for that component.
• In bookfuncs.js, send a "pre-login-complete" trigger/event instead of the "login-complete" event.
• In webpack.index.js, delay the runestone:login-complete trigger/event until dynamic loads are done and the "pre-login-complete" event has triggered.
• In renderComponent.js, when rendering a component, import its JS first.

I upgraded to webpack 5, so be sure to run a npm install then a npm run build to update everything when testing.

[bjones1]

Thanks! I think this will be a big step forward.