* Allow entry of a huggingface model id or civitai download url to be
done in the main model selection dropdown on SD tabs
* Remove separate textbox for entering huggingface model id or civitai
download url on SD Tabs
* Remove 'None' option from the model selection dropdown (no longer
needed) on SD tabs
* Update png metadata drop zone on txt2img tab to work with a single
argument for model selection
* Update UI generate functions on SD tabs to work with single argument
model selection
* Update API code for changes to the UI generate functions
* Move info about the custom model path to the logging textarea on SD
tabs
* Adds a button that opens the currently selected subdirectory using
the default OS file manager
* Improve output gallery handling of having images deleted out from
under it.
* Don't show VAE or LoRA lines in parameter info panel when their
value is 'None'
* Use a css class for small icon buttons on the output gallery
tab instead using the same id for multiple buttons
