preload_models.py script downloads the weight files

- user can select which weight files to download using huggingface cache
- user must log in to huggingface, generate an access token, and accept
  license terms the very first time this is run. After that, everything
  works automatically.
- added placeholder for docs for installing models
- also got rid of unused config files. hopefully they weren't needed
  for textual inversion, but I don't think so.

docs/features/INSTALLING_MODELS.md

@@ -0,0 +1,9 @@
+---
+title: Installing Models
+---
+
+# :octicons-paintbrush-16: Installing Models
+
+## TO COME
+
+