Add "None" option to extra networks dropdowns

[missionfloyd]

Adds a default "None" option to the Add hypernetwork to prompt and Add Lora to prompt dropdowns so the selection can be cleared.

Fixes #9707 Fixes #9024

Environment this was tested in

• OS: Windows 10
• Browser: Edge
• Graphics card: RTX 4070Ti

[jet3004]

Yep, 'none' only appears again if you go edit the config file...Thank you for posting this, has been driving me nuts.

[FurkanGozukara]

adding lora to x/y/z checkpoints would be great

[w-e-w]

adding lora to x/y/z checkpoints would be great

I don't see how your comment is related to the PR

and in case you don't know, you can use lora in xyz with s/r