Provide in each figure details on the used instrument

[jgieseler]

Similar to #59, add in figures info on the used instruments. For example in the multi-instrument tool, some panels already have that information (such as particle data), especially for PSP the data is shown for SPC and SPAN-i:

As the data can be different, it's important to provide for each plot info about the used instrument.

• SEP_Fit-Spectra.ipynb
• SEP_Multi-Instrument-Plot.ipynb
• SEP_Multi-Spacecraft-Plot.ipynb
• SEP_PADs-and-Anisotropy.ipynb
• SEP_PyOnset.ipynb
• SEP_Regression-Onset.ipynb
• SEP_Spatial-Distribution.ipynb
• SEP_Spectra.ipynb