Add mode for automatically numbering triplets

(Brought up in the comments of this post: https://musescore.org/en/comment/1072767#comment-1072767)

Add a mode to add/remove the "3" numbers from triplets according to common numbering schemes. I'm mot an expert in this field but two modes of numbering I think I have come across are:

• Only number the first triplet of a chain of triplets.
• Only number the first triplet in each line.

This mode should also work on other tuplets.