include social sharing links on confirmation page

This adds buttons to the checkinConfirmation page that allow the user to tweet/facebook share out the museum they're heading to. It will default to just sharing out CoolCulture social links.
Might it be better to get the museum from the checkin object?

If we do keep this, there's a bug with it. The checkin slug uses the museum name in the url. This is not necessarily equal to the museum slug and thus will fail.