Bug 1024507: Measure use of Twitter and Facebook

Dang, I just realized these calls need to happen **before** the  `ga('send', 'pageview' ...` call at https://github.com/openjck/kuma/blob/ad9d809600b25bd754d44270fdbf0c18d908992f/templates/includes/google_analytics.html#L49. `ga('send', 'pageview')` is what actually sends the data to GA.