Add noninteraction parameter for ga.js event tracking

* The ga.js version of track event supports an optional boolean parameter called 'noninteraction' that is provided for determining if the event is considered counted as an interaction for bounce rate. By default this
value is false, as per the ga.js spec, which infers the event is counted as an interaction.
* Added missing method headers for _trackEvent and _trackPage.
* All of the spacing in the readme is now consistent with the rest of the project.
* A little tuning to enable curly bracket checking all the time and remove obsolete comments.
* Added proper spacing after commas where it was missing.
* There was a lot of if (ga.js) { ... } else if (analytics.js) { }
statements throughout the code, but they weren't always consistent in
how they were defined. Replaced this with a callback style function call
to check and then execute if the appropriate script is loaded.
* Added a few more tests for trackEvent to test the non-interaction
parameter
* Improved trackPage and trackEvent tests to validate the ga construct
states.