LPS-51699 Cover Image for Blogs

cc/ @ipeychev @sergiogonzalez 
For this entire file, can you split the CSS into skin and structure sections like we do for the other css files in the taglib directory?
I've created some instructions for how I automate the process a bit, but of course, comment on the gist if you have any questions :) https://gist.github.com/natecavanaugh/bcefc9aba3d96d3cc79a#file-readme-md