Proposal: Add flip horizontal and flip vertical to the image rotate view.

[schnuti]

With only a few lines the flip functionality can be added to the image crop view. This is often used in particular if the base is an analogue image negative or diapositive where up and down/left and right easily gets incorrect.
Flip is included in the existing rotate events. A click on 0 degrees flips the image without rotation.
See gif animation. I'll add a PR later.

[laoneo]

Would be a nice addition!

[schnuti]

PR added

[laoneo]

We keep the issues open till it is finished and merged.