Add pinterest button and reorganize social sharing

First step in better social experience
I created one template for each social media (facebook, twitter, g+ and pinterest)
Also social media are only displayed when information is available

Finally, I corrected the facebook template which was using some unknown app_id...... that is user specific and needs to be set per user!
In fact, I think we can have this without an app_id, can we? By that, I mean Facebook does not require one, but I think it does in the default code...but it's not a big deal though.