11630 social links module

Here's a sneaky one for you: A new social links module

To test:
1. Pull branch
2. Go to blocks page and set the "Social links" block to show up in the sidebar.
3. Check out block, use contextual links "configure block" to add/remove social urls.

Once this is merged, we can work out how to remove the old social links block from install script & add this new one in.