Allow consistent pulsarfiles option in cwinpy_pe_pipeline configuration file

Currently, the cwinpy_knope_pipeline and cwinpy_heterodyne_pipeline specify the pulsar parameter files to use using the pulsarfiles option in the [ephemerides] section of the configuration file. However, the cwinpy_pe_pipeline uses the pulsars option instead. So, if you edit a cwinpy_knope_pipeline file to use it purely for subsequent PE it can cause problems unless you make the change. This MR allows either pulsars or pulsarfiles to be used in the cwinpy_pe_pipeline configuration.