DaSystem
DaPlatform
ObservationOperator

are now handled before the pipeline, from the das.py contents. This replaces the situation in which they were all 
constructed inside the pipeline based on rc-file items from the da.rc script. This now only serves to identify the 
cycle information, and no longer hold info about the platform, sampling model, and da system used inside a cycle.

Modified the method in which save/restart data is propagated. The observation operator now handles its own start/restart files in its private directory, and
passes the information of data that is needed for a restart to the DaCycle through a list. This list gets appended by all methods, and at the end all files of that
list are copied to the restart/current directory. The contents of that directory replace the restart/one-ago directory at the end of the cycle.