Add support for dragging an existing wire from one input port to another

**Is your feature request related to a problem? Please describe.**
Drag an existing link to a different port.

**Describe the solution you'd like**
If you have nodes A, B and C.
1. Link A to B
2. Click on the port at B to start dragging the same wire to C.

To achieve this right now, you have to delete the existing wire and create a new one.

**Describe alternatives you've considered**
This might conflict with the existing behavior of drawing multiple wires from the same port.