Add pitch changer

[Tofu86]

It would be nice if there was a pitch changer in Aimp equaliser, just like in NewPipe's (an open-source Youtube client/player) speed settings.

I like to experiment with songs' speed and pitch to make them sound "better" for myself. I can't always use NewPipe since I don't always have a good internet connection, and changing the pitch by myself for every song, every time, takes a lot of time.