Internal data points for OPC

Many of the OPC server's properties can be controlled by internal data points. Like every driver, the OPC client also uses an internal data point of type _DriverCommon. In addition to this data point, OPC-specific data points must also be used for displaying and amending properties of the OPC server and OPC groups. A data point of type _OPCServer must be present for each server used, and a data point of type _OPCGroup for each group used. The data points for the OPC server must be created before the OPC driver is started; the data points for the OPC groups can also be created during operation, and also be deleted again during operation. However, a group data point must be created before use in a peripheral address.