Correction for styleWithSpan setting

This correction makes sure that if I don't want to style with a span, it will not.  Previously this function was purely passive, and only enforced styling with spans...  a browser defaulting to css styling would continue to do so regardless of this setting.

This feature was used in response to issue https://github.com/HackerWins/summernote/issues/244 and is re-raised on issue https://github.com/HackerWins/summernote/issues/728.