Added the Bootstrap-recommended CSS normaliser (aka reset) for consistency...

Added the Bootstrap-recommended CSS normaliser (aka reset) for consistency across browsers, while removing reset content from other sass files.

Changed CSS-comments to SASS-comments so they aren't sent to the browser (bandwidth saving of 3kb approx). Left only the author/license comment and appended an 'END' comment.

- A basic visual check between using the normaliser and not using it, found a difference in *at least* one browser, [documented here](https://forum.f-droid.org/t/website-landing-page-revamp/6165/121), and
- Adds 2kb to page load.