Auto-refresh preview on file save

[Kernald]

Is your feature request related to a problem? Please describe.
This would help iterating quickly. Related to #81, currently, refreshing the preview is not super straightforward to do while working on the model at the same time. #81 soon being fixed will get us most of the way there, but auto-refreshing on file save would be even quicker. It would also match what a lot of instant reload style tools are doing.

Describe the solution you'd like
An option (the ability to be disabled probably matters for large models) to enable/disable auto-refresh on file save.

Describe alternatives you've considered
Clicking on the refresh button, which works but isn't super smooth.

Additional context
Add any other context or screenshots about the feature request here.

[ldenisey]

Will be done in #101