Add RemoteFileManager.parseChanges.
Fix bugs in remote_files.js introduced in the previous commit.
Add watchChanges and stopWatch methods to GoogleDrive.

Although https://developers.google.com/drive/v2/reference/changes/watch
says several parameters can be specified in this request as well as
changes.list, at least includeSubscribed=false has no effect. So there's
currently no these options available.
A simple GAE app to receive notifications and log them.