Add monmask

>> dso = add_monmask(dso,monitor_mask_file)

• [IXTdata_source] operation
• dso is an IXTdata_source
• monitor_mask_file is a string defining the location of the monitor mask file to be loaded, eg. 'X:\maskfiles\inst.mask' or 'inst_masks:::myfile.msk'
• this will add a monitor mask file location to an IXTdata_source object