Keyword Information: Add Means to Replace Post-Processor

This is a special purpose hook that is mainly intended to add a
post-processor after the keyword information is established only if
certain conditions are satisfied (e.g., if certain keyword relations
like the run using 'SGOF' tables hold).

Immediate use case is to install a post-processor for SOGCR to
subtract the scaled connate water saturation from defaulted SOGCR
values if the simulation run uses family I (SWOF/SGOF) saturation
function descriptions.

opm/parser/eclipse/EclipseState/Grid/GridProperty.hpp

@@ -21,6 +21,7 @@
 
 #include <functional>
 #include <string>
+#include <utility>
 #include <vector>
 
 /*
@@ -85,6 +86,11 @@ class GridPropertySupportedKeywordInfo {
         const post& postProcessor() const;
         bool isDefaultInitializable() const;
 
+        void setPostProcessor(post processor)
+        {
+            this->m_postProcessor = std::move(processor);
+        }
+
     private:
 
         std::string m_keywordName;