Change main board used as expansion to use Move task to prepare moves

[dc42]

On main boards used as expansion, currently the CanReceive task executes all CAN requests. This means that a high priority request such as movement can get delayed until a low priority request is complete. It would be better to use the same scheme as on expansion boards, i.e. CanReceive executes some commands immediately, puts movement requests in one queue which is emptied by the Move task, and puts other commands in a separate queue which is emptied by the Main task.