Ability to disable a SooperLooper action before it triggers

[riban-bw]

Is your feature request related to a problem? Please describe.
When SooperLooper is configured to trigger operations at sync points (quantised operations) the action is primed then waits in a pending state until the sync point. It may be advantageous to be able to deactivate such an action before the sync point triggers it.

Describe the solution you'd like
Toggle pending actions off by pressing the action button whilst it is pending.

Describe alternatives you've considered
Upstream project says that pressing undo will stop the action but this also performs an undo action which is not the desired behaviour. Could trigger and undo/redo cycle but this is prone to error. This also can change a loops play position resulting in out of sync playback.

Additional context
Upstream issue submitted.