introduce an "experimental mode"

this is a compile time switch with the intention to be able to more
easily turn experimental features that are not yet considered to be
production quality on and off. DUNE has a similar mechanism (i.e., the
`DUNE_GRID_EXPERIMENTAL_GRID_EXTENSIONS` macro), but it relies on
the preprocessor.

For now, the property does not have any effect.

ebos/ebos.cc

@@ -36,6 +36,11 @@ BEGIN_PROPERTIES
 
 NEW_TYPE_TAG(EclProblem, INHERITS_FROM(BlackOilModel, EclBaseProblem));
 
+// Enable experimental features for ebos: ebos is the research simulator of the OPM
+// project. If you're looking for a more stable "production quality" simulator, consider
+// using `flow`
+SET_BOOL_PROP(EclProblem, EnableExperiments, true);
+
 END_PROPERTIES
 
 int main(int argc, char **argv)

ebos/eclproblem.hh

@@ -325,6 +325,10 @@ SET_BOOL_PROP(EclBaseProblem, EnableThermalFluxBoundaries, false);
 
 SET_BOOL_PROP(EclBaseProblem, EnableTracerModel, false);
 
+// By default, simulators derived from the EclBaseProblem are production simulators,
+// i.e., experimental features must be explicitly enabled at compile time
+SET_BOOL_PROP(EclBaseProblem, EnableExperiments, false);
+
 END_PROPERTIES
 
 namespace Ewoms {