To be consistent with the general summary behaviour and more input
tolerant, 0.0 is returned when some phase, completion or well is
requested that isn't provided by the simulator.
Solves the issue discussed in https://github.com/OPM/opm-output/pull/122
and extends the test input deck to trigger this behaviour.
Introduces a simple format for data exchange between the simulators and
the the output facilities. Output functions will expect these types, and
it is the simulator's responsibility to create and provide it.
This patch introduces aggregates for well-related information: well
rates, bottom hole pressures and completion rates. Uses a simple bitmask
scheme to differentiate between written values and random garbage.
