Change default shortcuts for tenuto and marcato for consistency with shortcuts for staccato and sforzato (accent)

Currently, the default shortcuts for "toggle staccato" and "toggle sforzato" are, respectively, [Shift]+[S] and [Shift]+[V], while the respective shortcuts for "toggle tenuto" and "toggle marcato" are [Cmd]+[Option]+[N] or [Ctrl]+[Alt]+[N] and [Cmd]+[Option]+[O] or [Ctrl]+[Alt]+[O]. It would be a lot simpler and easier for the user to keep track of if the latter two were changed to [Shift]+[N] and [Shift]+[O].