Rotate signature in place

It shouldn't rotate around a corner but around the center of the signature block. This makes it easier to position the block first and then rotate, since rotating around the middle is easier to visualize in your head beforehand so you know where it will finally end up.

Without know much about how to do this in faricjs, there are two ways I can think of:

• move, rotate, move back
• set originX: "center", originY: "center" on the block, but this likely affects other operations as well I guess.

The easiest way to test this is to use the PDFs from https://gitlab.tugraz.at/VPU/Middleware/ESig/test-pdfs/-/tree/master/paper-size-tests which show a grid.