Bug fix, drag function added, modification finished

Bug: GridView getView() invoked mutipli times, causing bug in listeners.
Already avoided by using different listeners or not reusinng
convertView.
Bug remained: AppInfoLists duplicated for no reason, DK what causes it,
but no phenomenon now.
Bug remained: AppInfoLists sort by use frequency not finished, reflect
used, function doesn't work.
Modification finished: The end of this exercising project (hope so~),
cloned as a prp project to a new repository named "MetroLauncher",
futher modification may take place there.