Open Graph tags

I modified the title so that we provide cleaner titles for users. Also fixed HTML encoding for meta description (it used to break if there is a quote for example).

Adding OG tags is good for our integration with social networks:
- According to this, G+ reads OG tags: http://www.kingmoney.net/social-network/set-image-title-description-preview
- They are also used by other social networks: http://stackoverflow.com/questions/10397510/are-open-graph-tags-just-for-facebook

Issue: #293