Use a view pager to hold the different stats tabs. Makes it possible to swipe between fragments, and it is animated.
Revert "Use a view pager to hold the different stats tabs. Makes it possible to swipe between fragments, and it is animated."

This reverts commit 8fd4f23231792065b9e6208b998b3b41c5ece440.
Added a quick fade between fragment transactions in StatsAbsPagedViewFragment. Fixed janky replacement animation by setting the min height of the container to its current height.
Fixed up UX for StatsVisitorsAndViewsFragment:

 * Extracted out the bar char views into their own fragment. This allows the data below the chart to only be loaded once (instead of loaded in 3 separate fragments like it was previously)
 * Fixed wonky reload of bar chart data. Instead of removing all of the views, we just check for an existing bar graph and update its data if it exists.
Fixes margin between radio group and chart
Matching up tablet layout for stats visitors and views to use new container and radio buttons.
Removes unused instance variables. Props @nbradbury
Removed a ViewPager instance and TabListener that wasn't being used. Props @nbradbury
Merge pull request #784 from wordpress-mobile/feature/stats-ux-improvements

Stats UX Improvements