directory hiding for extra networks: dirs starting with . will hide their cards on extra network tabs unless specifically searched for
create HTML for extra network pages only on demand
allow directories starting with . to still list their models for lora, checkpoints, etc
keep "search" filter for extra networks when user refreshes the page

Do not call load_upscalers in list_builtin_upscalers

Why?
one of the internal calls of `load_file_from_url` import cv2, which locks the cv2 site-package, which extensions may (and in our case, is) breaking the installation of some libraries. The base project should be limiting its import of unnecessary libraries when possible during the installation phase.

use lowercase name for sorting; keep `UpscalerLanczos` and `UpscalerNearest` at the start of the list with `UpscalerNone`
Co-authored-by: Ncatboxanon <122327233+catboxanon@users.noreply.github.com>

os.path.getmtime(filename) throws exception later in codepath when meeting broken symlink. For now catch it here early but more checks could be added for robustness.

prevent .vae.safetensors files from being listed as stable diffusion models

add support for adding upscalers in extensions
move LDSR, ScuNET and SwinIR to built-in extensions

Child classes only get populated to __subclassess__ when they are imported. We don't actually need to import any of them to webui any more, so clean up webUI imports and make sure loader imports children.

Also, fix command line paths not actually being passed to the scalers.

Cleanup. Sorry.

Ensure we find checkpoints within subdirectories.

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.

Hook the model loader into the SD_models file.
Add default url/download if checkpoint is not found.
Add matching stablediffusion-models-path argument.
Add message that --ckpt-dir will be removed in the future, but have it pipe to stablediffusion-models-path for now.
Update help strings for models-path args so they're more or less uniform.
Move sd_model "setup" call to webUI with the others.
Ensure "cleanup_models" method moves existing models to the new locations, including SD, and that we aren't deleting folders that still have stuff in them.