Rounded icon unified

I've looked at the social icons and all rounded icons in general and figured out that we have some repetition there so the goal of this PR is to unify that.

It's introducing the `.rounded-icon` object which only purpose is to create rounded element so we don't need to copy same code across codebase.

So far it is taking care of `social-icons, live-indicator, gallery fullscreen icon, gallery share icons and autoupdate icon`. It can possibly include top navigation buttons, back to top button but I have to investigate further.

It saves astonishing 0.04 KB but the main advantage will be the better modularity.

![screen shot 2014-11-05 at 12 08 29](https://cloud.githubusercontent.com/assets/2579465/4918332/dc5d1828-64ef-11e4-9162-bb2e8aa4a825.png)
![screen shot 2014-11-05 at 12 08 34](https://cloud.githubusercontent.com/assets/2579465/4918330/dc5821ce-64ef-11e4-8217-0fc07a27145d.png)
![screen shot 2014-11-05 at 12 09 30](https://cloud.githubusercontent.com/assets/2579465/4918331/dc58f9b4-64ef-11e4-8375-1a58abf63368.png)
![screen shot 2014-11-05 at 12 15 39](https://cloud.githubusercontent.com/assets/2579465/4918333/dc6ef78c-64ef-11e4-930c-8be3ff9916bd.png)

CC @Jholder112233 @mattosborn especially @Jholder112233 if you can look at it if I didn't remove some important thing in the process