Make copying/moving of nodes easier

There are 2 ideas about making copying and moving operations easier:

1. Implement drag and drop for nodes
2. Implement ctrl+c/x and ctrl+v shortcuts

In my opinion we should implement both, and they share quite some backend functionality. I see some challenges for both:

In the d&d implementation:

• How to navigate and expand nodes while dragging a node
• After you drop the node, a popup must appear asking you whether you intended to copy or move the node (could we instead keep the ctrl key pressed when dragging to indicate we need a copy?)

In the copy/paste implementation:

• The UI should clearly indicate when a node has been 'cut'

In both approaches:

• You cannot give a new name to the node that you dropped/ pasted, unless we bring up a popup to facilitate this