Adding WPStats and WPStatsTrackerMixpanel.

WPStats will replace WPMobileStatsUtil as the new class to handle all
stats related calls in the Android app.
Adding some initial code to mixpanel tracker.
Added WPStats endpoints for themes and reader.
Disabling WPMobileStatsUtil's mixpanel calls for now.
Removing WPMobileStatsUtil unused event as it's a part of WPStats.
Adding WPStats tracking for stats.
Fixing crash in WPStatsTrackerMixpanel
Adding initial WPStats for editor related events.
Adding more WPStats for editor related events.
Adding WPStats events for notifications.
Adding WPStats for tracking the opening of various activities.
Adding WPStats calls for creating account and site.
Fleshing out WPStatsTrackerMixpanel.

Added in code to allow WPStatsTrackerMixpanel to perform actions on
the other possible things we might want to send to mixpanel (i.e.
people properties, super properties, etc.).
Adding WPStats tracking for view admin.
Clearing out mixpanel data on app end and logout.
Fixed bug where user's properties weren't being included in stats.
Adding in WPStatsTrackerWPCom to track a few WPCom stats events.
Removing WPMobileStatsUtil from project.
Adding in WPStats tracking for sharing a reader item.

Fleshed out the mixpanel tracking for a generic sharing item stat.
Removed the more finely grained ones we use in iOS as we seem unable
to track what the user shared to like we can in iOS.
Merge branch 'develop' into issue/1244-clean-up-mixpanel-implementation

Conflicts:
	src/org/wordpress/android/util/WPMobileStatsUtil.java