fix: correctly sort files, display deepest dir level first

[mashb1t]

There is an issue in the file sorting, which has to do with the condition of the lambda. os.sep returns correctly, but the sorting of the else condition just appends to the end and beginning, which is wrong.
This PR implements sorting for files when walking as well as topdown=False to display subfolders first.

Closes #1618
Relates to #1517

before:

after:

[wmlele]

Sort of related to this: is there any reason (security? isolation?) for not following symlinks to directories (followlinks=True) in the os.walk() call?

I don't think I am the only one to have an organized model store with lots of categories and symlinks to them. If nothing prevents it, could it please be enabled?

[mashb1t]

@wmlele path_checkpoints and path_loras can now be an array in the config, basically there is no need for symlinks now. Please check if this works for you.