This adresses two issues from T57918.
- Adds ability to shift-click to select multiple nodes, which is broken in 2.8 currently
- Fixes conflict with shift-click and Re-Route feature. Re-Route is now Shift-RMB.
- Fixes conflict with Ctrl-LMB, which is used both in the Box Select tool and Cut Connections. Cut Connections is now Ctrl-RMB.