add background picture for collage 1+3 and stailized rotary encoder

[DIY89]

Prerequisites checklist

• [x] I have read the contributing guidelines.

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

• [ ] Documentation update
• [ ] Bug fix
• [x] New feature
• [ ] Other, please explain:

What changes did you make? (Give an overview)

• Add new option for background picture for collage 1+3 and example background picture.
• Text on background can be added via the existing options
• Stabilized rotory encoder function to change the focus every third "click".

[andi34]

Hey and thanks for your contribution! Your changes don't cleanly apply to latest source, yesterday a bunch of collage improvements have been added. The collage background option was removed here https://github.com/andi34/photobooth/commit/eb4293e2f36b83e4220a3955488aaf8e27754bdc because we've decided to use a matching frame instead which will be applied on top of the images and allows to add decor elements onto the image instead hiding them behind. Your PR contains some more changes which I can not add to the repo (94 commits; 16 files changed).

You're able to add your rotary encoder changes on top of our latest dev branch and create a separate PR?

Best regards

Andi

[andi34]

Can't find the license of the background image, only looks like it's from HTC Wallpapers https://www.giga.de/unternehmen/whatsapp-inc/gallery/whatsapp-hintergrundbilder-11-wallpaper-zum-download/