Change the cursor to a Hand when above the spectrogram

[AlonKellner]

Background

Currently when the mouse pointer is above is spectrogram it still seems like an ordinary arrow, making it not obvious that clicking on it will do something.
We would prefer it if it would change to a hand icon instead.
This 👆 not ◀️.

Recommended Prior Knowledge

• Experience with Bokeh, HoloViews and Panel

Suggestion

I found a lead in a stackoverflow question, seems promising.

[ahuang11]

Here's how Toggle does it if it helps at all

https://github.com/holoviz/panel/blob/0d1391576ebbe0eeb668d088705e39411c7cfc61/panel/models/button_icon.ts#L12

[AlonKellner]

@ahuang11 That's probably precisely the solution, Thanks :)
I'll start working soon on a PR for the Beta with multiple responsiveness features, including this one