changed: remove embedded 'parameters' namespace in ParamGroup

inconsistent and unnecessary.

this is purely a cosmetic change, the only exception was a function with
the generic name 'split', which was renamed to splitParam to avoid confusion.

opm/core/props/BlackoilPropertiesBasic.cpp

@@ -26,7 +26,7 @@
 namespace Opm
 {
 
-    BlackoilPropertiesBasic::BlackoilPropertiesBasic(const parameter::ParameterGroup& param,
+    BlackoilPropertiesBasic::BlackoilPropertiesBasic(const ParameterGroup& param,
                                                      const int dim,
                                                      const int num_cells)
     {