Add an outline for blocks

[martinDolan]

This is a PR to fix #5

I've added an outline to be able to see blocks when they're in the editor and are either empty or have white background. I added the CSS to the global file since it's just a small amount. I could always add a separate editor file, but this seemed adequate for the moment.

[martinDolan]

@johnheimkes I've moved the CSS to its own file. Thanks!