Add a virtual CAN bus plugin

A virtual CAN plugin allows to send CAN frames from one app and receive them in another app with no CAN hardware involved.

While this is already possible with SocketCAN along with the SocketCAN plugin, this is limited to Linux.

A virtual plugin would allow to test under Windows or macOS also.

The virtual plugins could communicate over a local or internet socket (that would by the way show how to create a CAN-Ethernet gateway).

It has to be checked, if this new plugin could also replace the generic plugin which is used for the auto tests.