fixed the slipToPaddingRefresh bug
net connection considered and loading data in AsyncTask
firstVisibleItem is header view
network connection utils
utils to networkutils
add pullToRrefresh library
pullToRefresh in SampleListFragment
fix pullToRefresh bug TODO remove the tab to refresh above the header
view
add last update time in pullToRefreshListView
set last update time when complete
fixed adapter bug
when scroll to refresh, not show Toast message
only when click the retry button
and when drag to refresh under no net connection, show Toast message