New ReactOS Website: Add GitHub, Twitter, YouTube, Facebook, VK buttons

Add buttons to our GitHub page, Twitter feed, YouTube channel, Facebook page, VK page (in that order). Consider that the Universal theme we use already comes with an extra top menu bar for them, however we haven't decided yet if we want to use that additional bar or come up with something on our own.
Possibly try out the "Fork me on GitHub" banner in the top-right corner too.