Filesystem events

Currently there's no way to fetch real time filesystem modifications inside
webapps, both on FileLists or DirEntries. I propose to add filesystem
monitoring events to the DirEntries objects, so when a file or directory is
added, removed or modified a corresponding event would buble on the
filesystem hierarchy up to the DirEntry object where an event listener is
registered to catch it, so the webapp would act in correspondance (hashing
the files, uploading them...).

This would also be applied to the FileSystem API and the DeviceStorage API
(so for example files dropped on that folder would be uploaded and later
removed, in a mail box or printer queue style) and up to some degree on
FileList objects, too.