[Feature Request] Two Panes/ Two Notes

[DiagonalArg]

I'm often finding myself rejiggering my notes, in which I have to copy between two of them. Having two panes showing different notes would help. My untutored imagination suggests to me that the code for this would be also useful if/when markdown is introduced, as there will need to be two panes there also, one rendered and one unrendered.

https://github.com/giuspen/cherrytree/issues/218#issuecomment-620161230