Feature Ui music player: Add a "Loop" toggle button

[Gero5]

Except for the braces in the music envelope shape there is no indication wether loop is turned of or off. there is also no possibility to toggle loop from the UI other than pressing "L" on the keyboard.

Feature Request: Add a button called "Loop" or "Loop On/Off" below the music envelope. The button is highlighted when Loop is On. When clicked it toggles the Loop feature for ON to OFF and vice versa.

See also #1210 #1209

[mpogue2]

I like this idea. I'm thinking, though, that it should be a loop icon (as some of the other music players use), and it should be integrated with other stateful controls.

For example, here's Mixxx (SNAP and LOOP shown here are stateful controls):

Note: the Mixxx count there is not the "loop counter" you suggested, it's a "loop length", so here is where we would diverge from the Mixxx model.