Fixed file transfer cannot proceed caused by user deletes director…

[denven]

1. Added comments for better code review and understanding;
2. Fixed time string conversion error;
3. Fixed sendMetada dead loop (due to user deletion of google drive directory) which leads to file uploading failure;
4. Fixed sendFile failure (due to user deletion of google drive directory) which leads to current directory cannot be uploaded(1 hour's video files may not be uploaded at most);
5. Other trivial code modification.

• Replace GDriveUploader and reboot to test the new script (Some exceptions may not be covered).
• New script can be tested on the camera or a local Linux machine.