changed: build separate simulator binaries for flow

this is very convenient during development.
we can then remove the FLOW_BLACKOIL_ONLY option,
as it is no longer needed - use the flow_blackoil binary instead.
however we need to keep this support in Main.hpp due to the python
bindings relying on it.

flow/flow_ebos_oilwater.hpp

@@ -30,8 +30,13 @@ void flowEbosOilWaterSetDeck(double setupTime, std::shared_ptr<Deck> deck,
                              std::shared_ptr<EclipseState> eclState,
                              std::shared_ptr<Schedule> schedule,
                              std::shared_ptr<SummaryConfig> summaryConfig);
+
+//! \brief Main functon used in main flow binary.
 int flowEbosOilWaterMain(int argc, char** argv, bool outputCout, bool outputFiles);
 
+//! \brief Main function used in flow_oilwater binary.
+int flowEbosOilWaterMainStandalone(int argc, char** argv);
+
 }
 
 #endif // FLOW_EBOS_OILWATER_HPP