Simplify dist folder

[kr8n3r]

We're simplifying the dist/ folder by removing the component related files as they're currently not useful.

This can either be merged before or after next Frontend release
This PR:

• Updates the copy task to exclude component related files
• Updates tests that cover dist/ folder contents
• Updates build tasks that compile Sass and Javascript to build files in the correct location
• Insures only all.js is compiled to dist/
• Updates task that attached version to built assets
• Updates relevant documentation

To test:
run npm run build:dist

To test nothing changed in creating packages/
run npm run build:packages

Trello ticket: https://trello.com/c/faz4k1Pm/931-2-simplify-distributed-folder-in-govuk-frontend

[NickColley]

This is looking great but I don't believe the tests are checking that icons are copied correctly, is this something we want?

[kr8n3r]

true, we never wrote test for copying icons. separate PR?

[NickColley]

@igloosi I'll raise an issue