Draft integration with Google Analytics.

Unit tests pass but not yet used in production.

By default, all experiments log views and conversions to Google Analytics (if it is available) using custom events:

    https://developers.google.com/analytics/devguides/collection/gajs/eventTrackerGuide

Configuration options are specified as follows:

 - `googleAnalytics.enabled`

   Boolean. Global or per-experiment option. Defaults to `true` - set to `false` to disable Google Analytics integration:

        Myna.init({
          googleAnalytics: { enabled: false },
          experiments: [
            // ...
          ]
        });

   or:

        Myna.init({
          experiments: [{
            uuid: "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa",
            class: "myna",
            googleAnalytics: { enabled: false }
          }]
        });

 - `googleAnalytics.viewEvent` and `googleAnalytics.conversionEvent`

   Strings. Per-experiment only. Default to `"<uuid>-view"` and `"<uuid>-converison"` respectively where `<uuid>` is the UUID of the experiment. Use to customise the event name for the events logged when a variant is first viewed and when the user first converts:

        Myna.init({
          experiments: [{
            uuid: "aaaaaaaa-aaaa-aaaa-aaaa-aaaaaaaaaaaa",
            class: "myna",
            googleAnalytics: {
              viewEvent: "foo",
              conversionEvent: "bar"
            }
          }]
        });

   Both types of event are logged with the variant name as an argument.
Track reward events on Google in parallel with sending them to Myna, to ensure they get sent before the page unloads.
Extra logging
Merged support for Google Analytics