isInitialized_ check in codegen should get it's own method

Currently it's copy + pasted all over the place: https://git.gsi.de/silecs/opensilecs/-/blob/master/silecs-codegen/src/xml/fesa/fesa_3_0_0/fesaTemplates.py#L455

The following exists 3 times in the code:

        if( !isInitialized_ )
        {
            throw fesa::FesaException(__FILE__, __LINE__, "SILECS-Service not initialized yet - ${className}::setup needs to be called before any plc-interaction can be done");
        }

Should be a separate method checkInitialized() in order to do not duplicate strings