Add UI for managing app settings

[seruva19]

Some of the settings are only applied after UI is shown (model is loaded only on first click on "Generate", etc). Therefore, it would be nice to have opportunity to tune app's settings in UI (instead of CLI).
Also it might be crucial for users to store their session settings in a file and load them on app's start. Especially since changing some settings would require restart of whole app.

What should be done:

• Store settings in file (YAML)
• Read/save settings file
• UI for editing options (under "Settings" tab)
• Separate class (KubinOptions) for managing options and settings (currently CLI options are stored directly in argparse output, which is not convenient)
• Improve UX (currently switching option checkboxes is done server-side, therefore might feel slow and clunky)
• Clarify which settings require restarting app and which do not
• Method for restarting app, including gradio (perhaps by call to dedicated FastAPI route that will kill current gradio process and start new one? idk)