This adds Twitter and Facebook sharing using the "Build your own Tweet button"
and Share Dialog methods, respectively. Both are javascript and iframe free;
instead you link to a specified url. For Twitter customization arguments
are sent through query parameters. Facebook requires you to put open graph
meta tags at the shared url.

Right now the user has to ensure their badge is made public before sharing.
Nothing stops you from sharing a private badge, but that link will be broken
when people try to visit it.
Move template off items
Attach shareTokens to badge objects for backpack.html page, and use correct share url for social sharing
Fix share url
Change from single share modal to one share modal per badge
Add ajax public/private toggle to badge share modal
Disable social network share buttons for private badges, and add explanatory text
Update facebook open graph share metadata
Change explanatory text around making badges public in share modal
Tidy up share styles slightly
DRY out template a bit with a macro
Show twitter/facebook shares as the more commonly expected popup
Changing tweet text
Merge pull request #645 from stenington/590-591-twitter-facebook

Twitter/Facebook sharing for /mybadges badges