Statistics fixes

Implement SlidingTabLayout from [SlidingTabs Example on developer.android.com](https://developer.android.com/samples/SlidingTabsBasic/src/com.example.android.slidingtabsbasic/SlidingTabsBasicFragment.html), and stop using `recreateActivity()` method when reloading as this was causing issues with Fragments.

Fixes the following issues:
[2337](https://code.google.com/p/ankidroid/issues/detail?id=2337)
[2338](https://code.google.com/p/ankidroid/issues/detail?id=2338)
[2339](https://code.google.com/p/ankidroid/issues/detail?id=2339)
[2340](https://code.google.com/p/ankidroid/issues/detail?id=2340)