Correctness of Finite Volume SRHD Shocktube

The SRHD_FV application currently holds the SRHD shocktube. Jean-Matthieu asks

Well the question was if the result is correct or not. It looks nice but since we are no expert we didn't knew if it was also correct.

and indeed he is right. We had a conversation at https://exahype-dev.slack.com/messages/@jm/ which brought me to commits https://gitlab.lrz.de/gi26det/ExaHyPE/commit/9a01da27c2282c6fbd3273f8e5dfc54abc6a4ca1 (+ following ones) to implement primitive output at SRHD(_FV). We do have values significantly nonzero:

This ticket shall track the progress here.