Add support for CSSI space weather data

While working on improving orbit determination accuracy, I came across the daily space weather data combined by AGI: ftp://ftp.agi.com/pub/DynamicEarthData/SpaceWeather-All-v1.2.txt

It would be a nice addition for Orekit to be able to parse this data file because:

it is released several times per day, always has the same file name and contains data from 1957 to 2044 (estimated) -> it is possible to have it in the orekit-data folder and have it updated via the update.sh script
it contains all the data required to implement the DTM2000InputParameters and NRLMSISE00InputParameters interfaces: 3-hourly and daily Ap and Kp data as well as daily F10.7 flux.

I am not a Java expert so it might take me some time to develop this feature. Therefore if somebody already started working on this topic or wants to help developing this feature, contributions are welcomed :)

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