Minify CSS and JavaScript

This pull request minifies a number of CSS and JavaScript files, particularly those utilised as third party libraries.
This pull request affects issue #480 and #575.

An amazing tool I often use for image optimization is [Shrinkray.io](https://shrinkray.io/). This tool allows users to compress .png images contained in GitHub repositories with one click. It would quite likely be very useful for optimizing images when new listings are added to twofactorauth.org.