main_get_persistent_argv() returns the (reproduced) options which
should be passed to a new window.

Since the executable is not a directory, renamed utils_resource_dir()
to the more generic utils_resource_path(), and RESOURCE_DIR_DATA to
RESOURCE_PATH_DATA_DIR etc.

Windows only: also fix the locale filename support. The standard
utils_get_locale_from_utf8() does nothing, because it targets the glib
filename encoding, which is UTF-8. g_locale_from_utf8() must be used.