add log in uploadFile listener
fix loggin bugs in uploadFile listener in uploadFile.js
try to fix fronted bugs in showing message and drag and drop interactions flow bugs
try to fix drag and drop event bugs
try to fix drag and drop event bugs
try to fix drag and drop event bugs
fix click event trigger dropAndClickEventHandler bugs
try to fix click event bugs
test backend remove files
remove gridfs.remove
fix drop one item's bug
divide the event handler into two