[CSS] Restructure/Cleanup & better device scaling

In reference to issue #201 I decided to address the cleanliness of the stylesheets as well as improve browsing scalability from small phones to hig-hDPI devices. Outside of just cleaning up the CSS (and normalizing the structure), I also made changes to enhance the view of the catalog (for all devices), post form, ad banner, and other elements that impede mobile displays. Desktop browsing remains largely the same, though mobile browsing has been improved greatly.

To make sure that my changes do not conflict with future changes in reference to issue #201 I would like to work with whoever is performing the cleanup. I'm not sure how terse we should be in organizing the selectors, and some thoughts would be appreciated.

To see the latest changes, visit http://8chan.co/stem/ to see them in a testable format (does not include custom themes).