Add support for multiple separate style*.csv files

[MisterSeajay]

Description

• Add support for multiple style files, using a wildcard in the CSV file name, e.g. style*.csv; this allows users to split styles between different CSV files (e.g. photographic, illustrative, etc.) and use downloaded CSV files (e.g. the Fooocus style list) without needing to merge them into one single file.
• All code changes are within the styles.py file; no changes required elsewhere within the application to support this. Interfaces to exposed functions/methods have not been broken.
• Feature request: [Feature Request]: Allow use of multiple CSV files for Styles #14122

Usage

To enable the multiple CSV functionality it is sufficient to add or amend the --styles-file command-line argument to include a wildcard * in the CSV file name, e.g. --styles-file=\path\to\styles*.csv. This will load all files matching the wildcarded file name.

The styles drop-down groups styles according to the file they were loaded from and inserts markers within the list to indicate which file the subsequent styles have been loaded from.

Edited styles are pushed to the bottom of the list of styles (no change to existing behavior). When an existing style is edited and saved, it will be saved to the same file that it was loaded from. New styles are always added back to the default styles.csv.

If the command line argument is omitted, or points to exactly one file, then the default behavior of using just that one file is maintained.

Checklist:

• I have read contributing wiki page
• I have performed a self-review of my own code
• My code follows the style guidelines
• My code passes tests

[AUTOMATIC1111]

I am usually inclined to not want to add changes to the code unless there is demand for them... Can some users comment on desirability of this feature?

[w-e-w]

All code changes are within the styles.py file

well .... I can see that you have made changes too .gitignore
in the future put your local .gitignore in ".git\info\exclude"

no comment on whether or not this should be merged
but if this is going to be merged it should be Squashed

[MisterSeajay]

The feature request for this is my own. I hadn't created the Issue before, but I have now:

#14122

[w-e-w]

@cjj1977 please squash your commits

[MisterSeajay]

I can see that you have made changes too .gitignore in the future put your local .gitignore in ".git\info\exclude"

Apologies for my ignorance/bad etiquette! I have moved my customizations to ".git\info\exclude".

[MisterSeajay]

I didn't squash commits. Revoking this PR & will raise a replacement one, hopefully cleaner.