Copy function

[vivitekk]

Hi,
as I was taking some notes during my physical chemistry course, I thought it would be nice to have a copy function paired with the select function. It would make taking notes of some derivations much easier as it would allow to copy part of a previous line and write only the part that has changed.

I hope it's not very hard or time consuming to implement. Appreciate your work very much!

[AraxTheCoder]

This should be implemented by #937.
It's not really copy and paste for the moment but sufficient for the use case you described.
I plan on implementing a copy cut and paste selection feature when you can also manually drag the selection to a different page.