Menu option to open preferences directory

[talmo]

The user preferences get saved in a user data directory that's OS dependent. It would be handy to have an option (under Help? File?) to open the system File Explorer at that directory so people don't have to dig around their system paths to find it.

[gitttt-1234]

Note: Also update these routines that handle management of the preferences directory to use pathlib, and break it out into its own methods:

sleap/sleap/util.py

Lines 276 to 289 in 0528362

	desired_path = os.path.expanduser(
	f"~/.sleap/{sleap_version.__version__}/{shortname}"
	)
	# Make sure there's a ~/.sleap/<version>/ directory to store user version of the
	# config file.
	try:
	os.makedirs(os.path.expanduser(f"~/.sleap/{sleap_version.__version__}"))
	except FileExistsError:
	pass
	# If we don't care whether the file exists, just return the path
	if ignore_file_not_found:
	return desired_path

[talmo]

This was done in #1847 --> #1843