Permission denied errors

Hi!

In stm_lms_generate_styles() there are a couple calls to $wp_filesystem->mkdir() which have chmod argument set to 0700. In some hosting configurations this prevents the web server from having access to the styles directory and therefore these files aren’t readable. I think the explicit chmod should be removed in these cases and allow WordPress to use the default from the FS_CHMOD_DIR constant. This is a similar approach taken later in this same function with the call to $wp_filesystem->put_contents().