Scale function for layout

[kek444]

Added a simple layout scale function, which I needed on several occasions, usually when changing my mind about the print quality. Usage: press "Scale" on the layout options, enter the new DPI, check if you want the layout dimensions to scale also (in some corner cases you might not want to) and all the elements do a simple rescale and reposition, as if a "zoom" was performed.

[nhmkdev]

The Layout (context menu) > Resize Layout deserves this upgrade (as an option). I thought this already existed hahaha. I might move the code and juggle it. Undo doesn't work right with Resize Layout now so... that's something I should work on too.

[nhmkdev]

Pull request was not directly integrated but the core concept was. 👍