ENH: relocate zero_one to pTraits, allows reuse for scalar clamping

ENH: add pTraits and IO for std::int8_t

STYLE: cull some implicitly available includes

- pTraits.H is included by label/scalar etc
- zero.H is included by UList

STYLE: cull redundant forward declarations for Istream/Ostream

applications/utilities/mesh/advanced/selectCells/edgeStats.H

@@ -34,8 +34,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef edgeStats_H
-#define edgeStats_H
+#ifndef Foam_edgeStats_H
+#define Foam_edgeStats_H
 
 #include "direction.H"
 #include "scalar.H"
@@ -45,9 +45,8 @@ SourceFiles
 namespace Foam
 {
 
-// Forward declaration of classes
+// Forward Declarations
 class polyMesh;
-class Ostream;
 class twoDPointCorrector;
 
 /*---------------------------------------------------------------------------*\