Extend batching to global time stepping

I am currently working on extending the batching from "globalfixed" to "global" time stepping. The idea is here to only reduce the time step size and other data in the last iteration of the batch. If something went wrong, we then roll back to the state at the beginning of the batch. This WiP issue is for tracking my progress and issues I ran into.

Reduction of time step size

While we will not update the currently used CFL time step size in every single iteration in the planned batched global time stepping scheme, we will search the minimum CFL time step size over all batch iterations. This allows us to check if the used time step size did violate the CFL constraint during the execution of the batch. The consequence might then be to use the newly determined minimum batch time step size as time step size for a rerun of the whole batch.

Basic modifications to the fused time stepping algorithm

• We will store the previous solution only at the beginning of a batch. The same happens with the previous time stamp and time step size.
• TBC...

Rollbacks:

TBC...