Refactor all CSS

[ferrerluis]

Summary

There is a lot of stray CSS in HTML files around our code base. The idea is to take all of it and put it in app/assets/stylesheets/style.scss without breaking anything.

Also there is a lot of CSS that is there but is not doing anything and can be deleted. Additionally, we are now using SCSS (which is backwards compatible with CSS), so it means we can use extra functionality to make our code look a looot nicer.