Features/add google analytics

By adding support for analytics, we will be able to understand how the users are using the app. With that insight, we'll be able to make better decisions regarding which new feature to introduce and which existing feature to improve or phase out.

Gem used: [rack-google-analytics](https://github.com/leehambley/rack-google-analytics)

Please refer to [Event Tracking Guide](https://developers.google.com/analytics/devguides/collection/gajs/eventTrackerGuide) for understanding how events are tracked through [Google Analytics](https://developers.google.com/analytics/devguides/).