Changes for new libROM API

[jtlau]

Proposed Changes

Small updates due to changes in libROM API (corresponds to PR LLNL/libROM#80 )

PR Checklist

Put an X by all that apply. You can fill this out after submitting the PR. If you have any questions, don't hesitate to ask! We want to help. These are a guide for you to know what the reviewers will be looking for in your contribution.

• [ x] I am submitting my contribution to the develop branch.
• [ x] My contribution generates no new compiler warnings (try with the '-Wall -Wextra -Wno-unused-parameter -Wno-empty-body' compiler flags, or simply --warnlevel=2 when using meson).
• [ x] My contribution is commented and consistent with SU2 style.
• [ n/a] I have added a test case that demonstrates my contribution, if necessary.
• [ x] I have updated appropriate documentation (Tutorials, Docs Page, config_template.cpp) , if necessary.

[pcarruscag]

Do you need to list the new version somewhere?

[TobiKattmann]

Maybe have it as a submodule? Then the compatibility between SU2 and librom does not depend someone's knowledge which librom version has to be used.

[jtlau]

I'm going to pull this in for now, but I'll look into adding libROM as a subproject. libROM has a handful of prerequisites (hdf5, mpi, lapack, etc) so leaving it as a standalone project might be easier