Model Loader, Fixes

Yep.

Fix gfpgan_model_arch requirement(s).
Add Upscaler base class, move from images.
Add a lot of methods to Upscaler.
Re-work all the child upscalers to be proper classes.
Add BSRGAN scaler.
Add ldsr_model_arch class, removing the dependency for another repo that just uses regular latent-diffusion stuff.
Add one universal method that will always find and load new upscaler models without having to add new "setup_model" calls. Still need to add command line params, but that could probably be automated.
Add a "self.scale" property to all Upscalers so the scalers themselves can do "things" in response to the requested upscaling size.
Ensure LDSR doesn't get stuck in a longer loop of "upscale/downscale/upscale" as we try to reach the target upscale size.
Add typehints for IDE sanity.
PEP-8 improvements.
Moar.

Fixes bug where if Type is Nothing and axis values are filled out (from ie. previously using another Type), it will still needlessly run it N times (with identical results).

Changed the hidden element class name to a more generic one, so people can reuse it if they want to hide further elements in the future

Handling of the --hide-ui-dir-config flag and added multi-platform code for opening a folder