Provide support for old SolO/STEP data product

[jgieseler]

PR #33 introduces support for Solar Orbiter/STEP data for the onset determination, time shift analysis, and dynamic spectrum Notebooks, but only for the new STEP data product that is in use since 22nd October 2021. Extend this also for the old data product that has slightly different parameters. Note that this requires an update to solo-epd-loader to work (cf. jgieseler/solo-epd-loader#23)

[jgieseler]

solo-epd-loader has been updated, so the first step is done.

Note that now the old STEP data hs the same column naming syntax (but different amount of energy channels), so it should in principle be more or less compatible if the new STEP data is already working.