COSTEP-EPHIN: implement kor files (correction for p and He)

[jgieseler]

• Proton and helium measurements of SOHO'S COSTEP-EPHIN need to be corrected for effects determined post-launch, cf. chapter 2.3 of https://www.ieap.uni-kiel.de/et/ag-heber/costep/materials/L2_spec_ephin.pdf.
• Downloading of the .kor files (easy & analog to the .rl2 files) and the correction itself needs to be implemented!
• Until this correction has been implemented, these data products are set to -9e9 (cf. 5cb02f7#diff-0200c6387b73db45456b103bd7853fa746315b9385bb78c6338206a2c213ead0R343).
• Setting use_uncorrected_data_on_own_risk=True skips this replacement, so that the uncorrected data can be obtained at own risk!