Taal: Which initial conditions, boundary conditions, source terms should be exported?

[sloede]

IIRC, we started a small discussion about this in the past. There was a suggestion to distinguish "one-time throw-away" initial conditions etc. from "reusable and/or generic" ones, e.g. initial_conditions_linear_x vs. initial_conditions_convergence_test. The new possibility to define initial conditions etc. directly in the corresponding elixir_*.jl file makes this easily possible.

I think we should continue this discussion together. I'm not against keeping all current initial conditions etc., but we might as well move some things around.

Originally posted by @ranocha in #200 (comment)

[ranocha]

Superseded by #237.