Added visual separator between the wallet types on choose-your-wallet page

It took me a minute to understand why blockchain.info's icon was on the "choose your wallet" page twice, and I also remember wondering whether it'd be clear to users that some downloads are not desktop applications. I only understood once I saw the text above the icons.

Since many people don't read the all the text on a page (especially a page leading to downloads, and I came here looking for the bitcoin-qt download), I think this visual hint, separating the different client types with a gray line, makes it clearer that there is not only the choice of which wallet to use but also different types of wallets.

Screenshot of change (to compare with bitcoin.org/en/choose-your-wallet): http://imgur.com/PcCqIEO

I'm not that experienced with Github and how appropriate it is to do pull requests for such a small change, but I think it will help users so I'd like to contribute the change anyway. Thanks!