add UI selection for cross attention optimization

rework hires prompts/sampler code to among other things support different extra networks in first/second pass
rework quoting for infotext items that have commas in them to use json (should be backwards compatible except for cases where it didn't work previously)
add some locals from processing function into the Processing class as fields

fix Reload UI not working

add slider for token merging for img2img
rework StableDiffusionProcessing to have the token_merging_ratio field
fix a bug with applying png optimizations for live previews when they shouldn't be applied

only download TAESD model when it's needed
return calculations in single_sample_to_image to just if/elif/elif blocks
keep taesd model in its own directory

add a bit of spacing/styling to settings elements
add link info for token merging

Allow web UI to be ran fully offline

Allows web UI to (almost) be ran fully offline.
The web UI will hang on load if offline when
these fonts are not manually defined, as it will attempt (and fail)
to pull from Google Fonts.

change live preview format to jpeg to prevent unreasonably slow previews for large images, and add an option to let user select the format