Stats: Refs #874. Retains the selection under Visitors and Views tab when rotated.

The selection wasn't being saved and persisted when the fragment was destroyed and re-created.
Merge branch 'develop' of https://github.com/wordpress-mobile/WordPress-Android into develop
Merge branch 'develop' of https://github.com/wordpress-mobile/WordPress-Android into develop
Stats: Refs #874. Using setRetainInstance(true) retains the selection under Visitors and Views tab, when rotated.
Merge pull request #975 from anirudh24seven/develop

Stats: Refs #874. Retains the selection under Visitors and Views tab when rotated.