Add a propagate button to copy the (warped) contours from the template image to the selected overlay one

[zindy]

Hello,

this change adds the possibility to apply the current transformation to the contours in the source image and "propagate" them to the selected overlay, via a new button on the bottom right corner of the align window.

Not sure if "propagate" is the best name for this button but all the other buttons on the row are one word too. "Transfer" or "Transfer contours"? At least the tooltip has a longer explanation of what the button does.

Here's the post I made which describes the changes in more details: https://forum.image.sc/t/improving-the-qupath-extension-align-ui-hopefully/67390

Cheers, Egor