Add "Paste From Node Path" to scene tree

Add this:

To allow to paste a node from the node path currently in clipboard to some location in the tree:

https://www.dropbox.com/s/4x0exn4p2rlzkl7/copy-paste-nodes.mp4?dl=0

I find this incredibly useful if I need to replicate items at different positions in the tree.

Notes:

(1) only uses the node path; i.e. if the node name changes or another node takes its name, the copied item changed accordingly (so users need to know what they're doing) (2) only works inside one node tree (since only node paths are used)

This is currently a "paste before", such that ctrl+c + ctrl+v equals "Duplicate" and the pasted item always stays on the same level as the selected one; I also tried a "paste into", which is also useful, but maybe less intuitive for some people.