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!
This is out of scope, but @houndci is right here, everything has two extra spaces vs the first one.