Infinite Scroll: add Google Universal Analytics Support

Props @DeanMarkTaylor
Infinite Scroll: remove extra ]

See https://github.com/Automattic/jetpack/pull/789/files#r14565151
Infinite Scroll: refactor GA support

See https://github.com/Automattic/jetpack/pull/789#issuecomment-48062581
Infinite Scroll: add some spaces
Merge pull request #789 from jeherve/g_universal_analytics

Infinite Scroll: add Google Universal Analytics Support