First cut at social media icons

TODO

- Design
- Agreement on canonicalUrl implementation (ie. no editions)
- Sharing on galleries & videos
- Working tests
Working tests for each of the four social networks
Using canonicalUrl across articles, gallery, video pages
Typo
Style via Jim
Fresh text fixtures
Remove standfirst from fragment

LinkedIn does a good job of fetching this from the URL we give it.
Hide social icons behind a switch
Merge branch 'master' of github.com:guardian/frontend into share

Conflicts:
	common/app/conf/switches.scala
Remove println
CSS tweaks to icons
Remove outer div & added common social-network class
Merge pull request #493 from guardian/share

Share buttons