Add averaging fields for output in restart files

[JorgSchwinger]

Currently, if iHAMOCC is stopped/restarted, the averaging information for output files that have not yet been written is lost. E.g. if IHAMOCC is stopped end of June and restarted 1st of July, the annual output for this particular year will be incorrect (containing only the average July-December). To fix this, the fields saving the average output need to be written to restart.

I consider this relatively low priority, because it is rarely needed for ESM scenario simulations. It will be needed for data assimilation purposes, so when NorCPM upgrades to the current version of the iHAMOCC code, this will be needed.