Cleanup and Optimize

Here are some things which can be done to improve page load speed:

* [x] Caching: use caching with an `ETag` header. (was broken)
* [x] Utilize HTML5's application caching.
* [x] Images: convert all image assets to: 
  * [x] `svg` or
  * `webp`. (skipped)
* Split CSS Files: I know that downloading all CSS files in one go is a great idea, but it is not worth the time when 72% of the rules are not used on the current page. Here a great article about the matter. <https://www.igvita.com/2012/06/14/debunking-responsive-css-performance-myths/> (skipped)

General Improvements:
* [x] Change the log and cancel buttons to something more understandable. Maybe we can use [fa-times-circle](http://fontawesome.io/icon/times-circle) for cancel.

Please post any thoughts or suggestions.