Retracker command

Hello

When a tracker is changing its URL or when closing, it will be useful to batch change announce list.

So we can have
```bash
imdl tracker add https://some-tracker:12345
imdl tracker remove https://some-tracker:12345
imdl tracker replace https://some-tracker:12345 https://some-other-tracker:54321
imdl tracker set http://tracker1:12345,udp://tracker2:7654
```