Separate line for single note cresc/dim

https://musescore.org/en/node/279878

If we could have an articulation or a line that is opposing hairpins, it would solve a lot of notation issues involve dynamic changes on a single note. Currently, you have to adjust hairpins manually to get the right effect, and if the length of the measure changes, manually adjust again. It'd be great to have a palette option do it for you.