Building editor-styles.css

[remkus]

As soon as we can, we need to start to import the relevant bits of CSS from the general stylesheet into editor-styles.css

[GaryJones]

I've found that one of the easiest ways was just to @import style.css and then tweak a few bits to fix widths etc. Eases maintenance by not having to keep typographical and other styles in sync with style.css output.

[remkus]

I've already got a version going that's based off of what Twenty Fourteen does. Haven't got it ready just yet, but hoping to finish that up this week.