Fixed Open Graph image meta tags

According to http://docs.shopify.com/manual/configuration/store-customization/social-media/facebook/why-do-i-not-see-the-right-image-on-facebook
Facebook does not detect URL independend images. I adopted the shopify solution to work with bootstrapify.
the logo will typically not work with Facebook because it will be smaller than the expected minimum of 200x200px
Merge pull request #222 from adler99/master

Fixed Open Graph image meta tags