CSS cleanup / Mobile style improvements

-Rewrote style.css as mobile-first 
-Mobile no longer has horizontal scrolling issue (mainly on tiny devices)
-Mobile post form now fits on the page rather than overflowing, and will scale up to normal size on tablet or larger devices.
-Categorized the selectors (might make it easier for beginners)
-Removed a shitload of unneeded padding
-Images scale depending on screen resolution, but will be a fixed size on tablets or larger devices.