duplicacy should retry on network disconnections ("ERROR UPLOAD_CHUNK Failed to upload the chunk")

Every time I get disconnected from the wifi, or switch from one wifi network to another, or if I switch the VPN, or if there is some kind hiccup on the network, duplicacy fails and completely gives up with:

```
ERROR UPLOAD_CHUNK Failed to upload the chunk
```

This is a usability problem.  Ideally I shouldn't have to monitor the backup upload.  It should just work and retry on network errors.