feat: Add folder selection functionality for model directories.

[LlamaEnjoyer]

Another (hopefully) useful qol feat: users can now manually point to the model folder via button:

[turboderp]

I'm a little unsure about this one. I had originally wanted a folder select button, but browsers simply don't allow it (for obvious security reasons.) Using tkinter is one option, but launching a dialog on the server wouldn't really work if the server and client browser aren't running on the same device. I know a bunch of people use headless servers, or even cloud servers, so I'm just not sure this is the right approach.

[LlamaEnjoyer]

Understandable, I can always keep it on my own branch for private use. If you ever think of a better approach feel free to pont me there and I'll see if it's something I can implement :)