Add ability to reorder folds

[VeraZab]

closes: #717

[VeraZab]

@nicolaskruchten I think this is what we want would you check please ✨
I didn't add it to other accordions, but this easily could be extended to them

[VeraZab]

@dmt0 I think this is ready for code review as well

[VeraZab]

adjusted styles

[VeraZab]

so I've added the ability to reorder: images, shapes, annotations on top of traces

for transforms, I wasn't sure about the array to reorder (it changes based on the transform applied, and I'm not sure of the side effects) so I didn't do it here.

for rangeselector buttons, the path to get to the array to reorder is a bit less straight forward. I could perhaps use the nested property function of plotly.js. but didn't do it here.

just picked the low hanging fruit. let me know if that's ok @nicolaskruchten

[dmt0]

💃 !

[nicolaskruchten]

✨ although I don't love the "you can't click here" cursor on the greyed out arrows... I'd just leave it as a normal non-link cursor.

[VeraZab]

although I don't love the "you can't click here" cursor on the greyed out arrows

yeah, agree, removed!