Call onBlogChanged when there are blogs visible in the app
Make sure currentBlog is not null in StatsActivity when onBlogChanged is called.
Call onBlogChanged if currentBlog is not null
Revert "Call onBlogChanged if currentBlog is not null"

This reverts commit f63d1ee322bab8f3fb180dd69e52a3919dfa95f9.
Revert "Call onBlogChanged when there are blogs visible in the app"

This reverts commit e1df5508b7611cc921dc854e60727b0360114d95.
Refactored 'onBlogChanged' that now is called in descendants of WPActionBarActivity when currentBlog != null
Merge pull request #1904 from wordpress-mobile/issue/1901-NPE-StatsActivity-onBlogChanged

NPE in StatsActivity.onBlogChanged()