Bug 1024507: Measure use of Twitter and Facebook

Luke organized the logic so that Google Analytics event calls would work
correctly [1]. His commit was squashed into the prior commit to maintain
a history of working commits.

[1] https://github.com/groovecoder/kuma/commit/4bbd5f89e3539faeecdcbdb850c45508e265b709
Merge pull request #2734 from openjck/1024507-twitter-facebook-research

Bug 1024507: Measure use of Twitter and Facebook