Fully fledged flip implementation

[Janneman84]

I'm working on some new features and improvements, including a decent flip implementation.

While working on this I noticed some issues with the photo tending to slightly shift and jump after the rotate animation and cropping. You'll need to zoom in the photo a bit first to see this. My flip implementation had similar issues.

I noticed the code literary has dozens of floors, ceils and a few integer downcasts. I realized this probably was the cause of these issues. So I decided to just remove them all. Then I added pixel rounding where necessary, rounding to the nearest physical pixel (not point).

Doing this fixed all the issues I was experiencing, creating a more smooth and precise experience.

I have few other tweaks and fixes lined up as well, which I'd like to propose after this.

[Janneman84]

Turns out CGFloat and NSTimeInterval are both doubles these days. I'll make the necessary changes.

[Janneman84]

Ok I got rid of all of the float stuff, it's all doubles now :P

[Janneman84]

I included my fully fledged flip implementation:

For this I added two extra buttons. The vertical flip button is hidden by default. I changed the order of the buttons to make more sense. I replaced all pre-iOS13 buttons with images for consistency.

I had to update the delegate methods/callbacks with an extra 'flipped' argument. The old delegate methods still work for compatibility. In order to motivate developers to update I made it so fresh builds (less than 2 hours old) will crash when opening the cropper, telling you to update the delegate methods. So once released it won't crash anymore.

I have a bunch more tweaks and fixes in the works if you're interested.