WIP paypro: add floating merchant box.

Not really a real pull request. More of a proof of concept. The CSS doesn't respect media queries, mobile css, etc.

But here are some screenshots of what the payment protocol merchant box could look like after clicking the valid checkbox:

Payment Protocol URI has been entered - checkbox turns a different color:

![](http://i.imgur.com/ZhO1MrU.png)

Checkbox has been clicked (:focus) - The absolutely positioned merchant div is displayed:

![](http://i.imgur.com/DVoOWte.png)