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
Fix #322: add a _visit security settings_ button that open a browser in WordPress.com->Settings->Security to create an app specific password when 2FA is enabled and master password entered
Merge branch 'feature/nux-improvements' into issue/322-better-ui-2fa-detected
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
Merge branch 'develop' into issue/322-better-ui-2fa-detected

Conflicts:
	src/org/wordpress/android/ui/accounts/TutorialActivity.java
Open Notifications links in webview
Do not show "sign out" and "settings" menus in the webview
Use constants when setting bundle extra items.
Increased padding in notification list, added timespan
Notification timestamp is now cached
Fixed bug that caused date not to appear on comment detail
Fixed misaligned note icon
Added a margin to the list divider used in notifications, posts, comments, etc. Tweaked comment row layout to match up to 16dp left and right margin.
Merge branch 'issue/362-notification-list-margins' of https://github.com/wordpress-mobile/WordPress-Android into issue/362-notification-list-margins