Add ExtendedCall to PLCObject as a replacement of RemoteExec and reflect it in eRPC interface.

ExtendedCall is a generic remote procedure call that runtime code can register to and that IDE extensions can call.
For example a fieldbus extension can use ExtendedCall to browse the fieldbus devices connected to the runtime.

                  <xsd:element name="OSX">
                    <xsd:complexType>
                      %(toolchain_gcc)s
                    </xsd:complexType>
                  </xsd:element>