Defer loading of the bokeh plot script

[Jhsmit]

In the GoldenTemplate, the golden layout library dynamically populates the bokeh DOM nodes. However, Bokeh executes this before these DOM nodes have actually been added.

Currently the fix for this is a hack which initializes the GoldenLayout even though the document is not ready:

  Object.defineProperty(document, 'readyState', {
    get() { return readyState },
    set(value) { return readyState = value },
  });
  document.readyState = 'complete'

However, ideally in the future we should somehow get the Bokeh plot script to defer loading until some condition is met.

See also the original issue: https://github.com/holoviz/panel/issues/3062

Also, and I'm not sure if this changes things; we are currently using GoldenLayout 1.5.9 but version 2 is also available: https://golden-layout.github.io/golden-layout/

Which is a complete rewrite in TypeScript + code cleanup + some API changes.