[FEATURE] Allow JupyUvi in to run in daemon mode

**Is your feature request related to a problem? Please describe.**
I am using `JupyUvi` inside notebooks for testing with `nbdev`. When a test fails in the middle of the notebook, `JupyUvi`'s `server.stop` is not called. Because the server runs the thread in non-daemon mode, the thread interrupts the process shutdown so`nbdev-test` hangs whenever something fails.

**Describe the solution you'd like**
I would like to be able to run the server in daemon mode. That way the parent process `nbdev-test` can kill it on exit after a brief wait. This *could* leave some open resources but given that the goal is to use it in notebook testing I feel it is acceptable. For "regular" use you can always run it in non-daemon mode to make sure it blocks before exiting.

**Example code**
Provide an example of how you imagine the feature working:

```python
srv = JupyUvi(daemon=True)
```

**Problem solved**

Process hanging due to missing `server.stop()`

**Confirmation**
Please confirm the following:
- [x] I have checked the existing issues and pull requests to ensure this feature hasn't been requested before.
- [x] I have read the project's documentation to ensure this feature doesn't already exist.