stabilized rotary encoder handling

[andi34]

Prerequisites checklist

• [x] I have read the contributing guidelines.

What is the purpose of this pull request? (put an "x" next to an item)

• [x] New feature

What changes did you make? (Give an overview)

• Stabilized rotary encoder function (Jump on every third "turn-click" to next button)

Is there anything you'd like reviewers to focus on?

Cleaned up https://github.com/andi34/photobooth/pull/441

[DIY89]

Yeah - that's a really good idea to integrate a slider to expert view. I also thought about this solution.