* Now removes identical copies without asking
* Now obeys `--dry-run`
* Implement `--dedupe-mode` for non interactive running
* `--dedupe-mode interactive` - interactive the default.
* `--dedupe-mode skip` - removes identical files then skips anything left.
* `--dedupe-mode first` - removes identical files then keeps the first one.
* `--dedupe-mode newest` - removes identical files then keeps the newest one.
* `--dedupe-mode oldest` - removes identical files then keeps the oldest one.
* `--dedupe-mode rename` - removes identical files then renames the rest to be different.
* Add tests which will only run on Google Drive.