remove the ptr tip
remove unused mContext
Post list: add refresh button in collapsed action bar
Prepare use a broacasted refresh event
fix #1321
fix #1320: onPostClicked can be called from a separate thread,
this thread can run after the activity onStop() and in this case,
commiting the fragment will crash the app.

Replacing a call to `commit()` by a call to `commitAllowingStateLoss()` in
this particular case, will avoid a crash but also lose the fragment state:
the selected comment or post won't be recreated.
Revert "fix #1321"

This reverts commit 6576d7f623a972f9c6979691f0bcc44af52dc240.
Revert "fix #1320: onPostClicked can be called from a separate thread,"

This reverts commit 19732b4aab3fe83d99805e75b70488dc836f824d.
add refresh button in most menus
broadcast refresh action
add PullToRefreshHelper register/unregister in all activities/fragment that could be refreshed
show a toast with a tip message when the refresh button is used 1/5/10/... times