Rhythm mode: duration command should use pitch of previous note where possible

A number of requests over the years in the forum have started to solidify in mind as one simple request:

In rhythm mode, currently the duration commands always enter notes on the middle line,. This is because we assumed people would enter a complete phrase first, then go back and use repitch mode. But we were wrong. I mean, people do this, but they also want to be able to repitch notes as they go, using the up/down keys. And for this purpose, copying the pitch of the most recently entered note makes way more sense.

For people using rhythm mode as originally conceived, this change is a no-op - the previous pitch will still be the middle line. But for people who change pitch using up/down, this is an enormous time saver, as the pitch of the next note is much more likely to be close to that than to the middle line. This ends up being a "poor man's Capella" mode, behaving almost as if the note input cursor could be moved vertically from line to line.

See https://musescore.org/en/node/306781 for further discussion and some links to previous threads.