Add feature to change the volume with scroll button over the volume volume-bar

[fabienmorin]

many other player do that, it's user friendly and would be nice to have it too in cozy-music

[jsilvestre]

Great idea! Thank you for suggesting!

[flyingrub]

#121 fixed

[fabienmorin]

Hi, thanks for the fix. It works quite well on chrome for me but on FF, it is just lowering the volume whatever the sense I roll the wheel. I found that interesting documentation by looking for this problem, may be that could helps.

For an easier use, I would propose to extend this behaviour not only to the volume-bar div block but on the whole controls-extended div block. Then it is no required to be exactly on the small volume bar to change the volume level, see #122.

[jsilvestre]

Oh! I just realized you did this PR, thank you very much! I had the same suggestion and asked @ysa000 to fix it (see #128 :p)

@m4dz and @ysa000, can I let you deal with this please?

[fabienmorin]

I see. Anyway, my code proposal was not working.