Prepare support for DD intervals in BDA DDECal step
This MR moves functionality related to DD intervals from the DDECal class to SolutionWriter and Settings class, so that it can also be used by BdaDDECal. This is a first MR to keep the MR size manageable. What this doesn't yet do is to prepare the solver data with dd intervals for the solver; a TODO is added for this in the code.
Edited by Andre Offringa