add option for disabling the spinner

[pwinckles]

It would be nice to have an option to disable the spinner similar to how colors can be disabled. The spinner produces output like the following in some environments:

[K⠋ waiting
[K⠙ waiting
[K⠹ waiting
[K⠸ waiting
[K⠼ waiting
[K⠴ waiting
[K⠦ waiting
[K⠧ waiting ....