Adding mixpanel lib to the app.

Creates a single mixpanel instance on the Application.
Refs #288.
Abstract stats wrangling into its own class.
Adds Quantcast lib.

WPMobileStatsUtil is patterened off the iOS version.
Corrects argument order. Adds documentation.
Adds const for quickphoto event.
Adds stats tracking for posts.

Updates some consts to represent properties instead of events.
Adds new properties and events.
Refs #288
Use onTouchListener instead of onClickListener.
Fixes the constant used for mixpanel token.
Flush events when tracking saved properties. We typically do this when an activity is destroyed so its a convenient way to sync.
Merge branch 'develop' of https://github.com/wordpress-mobile/WordPress-Android into feature/mixpanel
Adds platform property.

Fixes typo.
Adds pages opened property.
Merge branch 'develop' of github.com:wordpress-mobile/WordPress-Android into feature/mixpanel

Conflicts:
	build.gradle
Merge pull request #361 from wordpress-mobile/feature/mixpanel

Feature/mixpanel. Adds stats tracking for mixpanel for posting related activites.