Prefetch code editor files

[isglass]

To hopefully have it available when user opens the editor, without affecting load time for other more high prio resources.

https://developer.mozilla.org/en-US/docs/Web/HTML/Attributes/rel/prefetch

<link rel="prefetch" href="code-editor-file.js" />

Looks like it is mainly a few files that needs prefetching, the others are small: