[Users] Example parameter files / test cases and EOS_Omni changes

Dear Einstein Toolkit users

Many of the Einstein Toolkit hydrodynamics example parameter files and test cases do not work any more because thorn EOS_Omni is not activated and the corresponding parameters are not set. This is something where everybody can help, and it is important in the long term to have working test cases.

I suggest that we add to the Wiki a description of how to update a parameter file (which thorns to add/remove, how to modify parameters). We can then take the existing parameter files and update them.

-erik