Update asset build process

[vidurb]

The build process used in Third Eye was using tailwind and vanilla CSS. I'm wondering whether you think there's any value in adding more flexibility to the boilerplate. E.g.:

• Adding support for sass/less
• Adding PostCSS utilities to the vanilla CSS configuration
• Making tailwind optional during the install process so that if a project is to use some other framework Tailwind doesn't have to be removed before the other framework is added

These options could be implemented through composer scripts as the most basic implementation,or a PHP installation script could be written that would allow for a more robust implementation.

Personally, I think there should be optional sass support, tailwind should be optional during installation, and also, for the vanilla CSS option, we might as well add in postcss-preset-env so newer CSS syntax can be used since we're already using PostCSS plugins (autoprefixer, postcss-import).