Request: Stop pushback before connecting

[sandpatch]

The standard procedure at many places is not to connect the Pushback until GPU has been disconnected. There are varying reasons for it. E.g: To avoid bumping the cable and making it disconnect To make it easier to disconnect it To avoid Pushing back with the cable connected, etc.

It would be nice if there was a possibility to call the pushback but not to connect it and just have it wait in front of the plane. Only to connect after an order is given. This shouldn't interfere with the current voicepacks as there are separate recordings or both actions. Maybe even auto-connect it when the GPU is disconnected. As of now the pushback drives up and auto-disconnects the GPU.