This commit ensures that compute inter-region flow rates on all
ranks and collect those on the I/O rank using CollectDataToIORank.
We add a trivial EclInterRegFlowMap data member to the communication
object. This data member only knows the pertinent FIP region array
names, but uses existing read/write support to collect contributions
from all ranks into this "global" object. We then pass this global
object on to the summary evaluation routine.