Write out EPICS records to file

Add a method or to pydarm.darm.DARMModel or argument to pydarm.darm.DARMModel.compute_epics_records() that saves the EPICS records to a file like: epicsrecords_<ifo>_model<date>_create<date>.txt.

Let's also save the data as %.6e as engineering format with 6 decimals of precision for the front end EPICS