remove unused code
fix #1883 measure time in seconds between application_opened and application_closed
put signOut in an AsyncTask and show a ProgressDialog
use the asyncSignOut in WPActionBarActivity
use the asyncSignOut in PreferencesActivity
`NotificationsDetailListFragment` now listens for note changes.

List will refresh if the currently viewed note was changed. Detail view will pop back to list if the note was removed.

Also added a note changed listener, so that `CommentDetailFragment` can be notified when the note changes and update the comment and moderation buttons.
Merge pull request #1894 from wordpress-mobile/issue/1883-application-opened-time

fix #1883 application opened time
Added a null check on `getActivity()`
Merge pull request #1893 from wordpress-mobile/issue/1890-notification-detail-changes

`NotificationsDetailListFragment` now listens for note changes.
don't send BROADCAST_ACTION_SIGNOUT from removeWpComUserRelatedData()
null check mProgressDialog before dismiss and use local context instead of getContext
Merge pull request #1895 from wordpress-mobile/issue/1796-signout-lag

fix #1796 signout lag
Added context null check to reader service, WelcomeFragmentSignIn now uses the application context when starting the service.
Merge pull request #1902 from wordpress-mobile/issue/1898-npe-reader-service

issue/1898-npe-reader-service
fix #1897: null check mBucket onResume/onPause
Call onBlogChanged when there are blogs visible in the app
Make sure currentBlog is not null in StatsActivity when onBlogChanged is called.
Removed mPagerAdapter, now creating new pager adapter when needed and removing previous adapter before assigning to ViewPager
null check mNotesAdapter onDestroy
Call onBlogChanged if currentBlog is not null