Add a setting to toggle radial menu between advance on hover / advance on click

[scottanderson]

The current behavior of the radial menu is to advance to the next layer on hover. This makes sense for touchscreen, and possibly for trackpad, but is awkward with a mouse. Please add a setting so the user can choose between these behaviors.

[VariableVince]

Wanted to add that while i agree there could be a setting for those preferring different behavior, the statement 'but is awkward with a mouse' is subjective. As a mouse user, i like the hover feel in the radial menu for instance.

[evanpelle]

I'm working on PR to disable the back button from getting triggered on hover, since i find myself accidently going backwards all the time.

[scottanderson]

Partially addressed by #1330