Use dynamic import to load LiteMol package

[mirandaio]

This PR uses a dynamic import to load the LiteMol package. Doing this will extract the LiteMol code into a separate .js file which will only be loaded when a user wants to see the LiteMol structure in the app. Doing this reduces the initial JS code that is loaded into the browser when a user first visits the app, hence providing faster loading times.

The table below summarises the file sizes:

Code splitting	Files	minified	minified and gzipped (what Netlify serves)
No code splitting	main.[hash].chunk.js (app code)	245 KB	69.06 KB
	2.[hash].chunk.js (libraries with LiteMol)	4.5 MB	1.29 MB
With code splitting	main.[hash].chunk.js (app code)	245 KB	69.17 KB
	2.[hash].chunk.js (libraries without LiteMol)	3.2 MB	981.63 KB
	3.[hash].chunk.js (LiteMol)	1.3 MB	340.3 KB

[peatroot]

LGTM!