✨ Add octave displacement for clefs

[jinh0]

Fixes #648 .

demo.mov

Before this PR can be merged, there's one issue:

@annamorphism or @JoyfulGen , what is the minimum / maximum octave a neume can be? Currently, clef displacement has free reign and can lead to neumes having a -1 octave. From my testing, the maximum octave a neume can be is 6.

[annamorphism]

@jinh0 You mean, in what it can do in Neon, or what it might represent musically? Assuming middle C=C3, chant never goes outside the range G1 to E4 (and even that's pretty generous really). So while you can currently give neumes all sorts of octaves, it really only makes sense to have them go from 1-4.

[jinh0]

Hey @annamorphism , sorry, to clarify, this new feature in Neon allows you to have pitches displaced down to F-1 all the way up to C6.

If it doesn't make sense musically, should Neon restrict the user from displacing neumes to pitches below octave 1 / above octave 4?

[annamorphism]

@jinh0 I mean, a range from -1 to 6 is pretty sensible and won't break anything. you could make it even smaller if you wanted to, though.

[yinanazhou]

• the dropdown menu for clef shape change is not functioning
• the HTML part for two dropdown menus for clef contains several repeated id attributes