Configure code splitting to reduce loading time for output files

[taspeotis]

Looking at the demo site it takes about 16 seconds to load.

I think theme.js could go on a diet, since a cursory glance shows it's not minified.

[azaslonov]

Hi @taspeotis, the quick fix for it would be to switch webpack mode to "production" here.

The longer fix would be to switch to the code splitting approach, which is coming a bit later.