Feat: Copy and paste elements into the canvas

[sandstone991]

A user should be able to select one or more elements, copy them and paste them wherever the cursor is at that time.

• Should be able to validate the structure of the pasted content to detect whether they are zagyElements or not
• Should find a solution for asking for clipboard permission (other vendors seem to have it solved)
• Should be able to paste across different instances of the page

The elements will need to be recreated since you wouldn't be able to transform things like canvases or Path2d into a string

[sandstone991]

Attaching a global paste event seems to have done the trick

[nagy-nabil]

copy and export scene in #61