ENH: mutable libs() access in Time and other classes (#1737)

- This reflects the pre-existing coding situation where const_cast was
  used throughout to effect the same.

STYLE: fix private/protected access

- CodedField, codedMixedFvPatchField

src/dynamicMesh/motionSolvers/displacement/codedPoints0/codedPoints0MotionSolver.C

@@ -89,7 +89,7 @@ void Foam::codedPoints0MotionSolver::prepare
 
 Foam::dlLibraryTable& Foam::codedPoints0MotionSolver::libs() const
 {
-    return const_cast<Time&>(mesh().time()).libs();
+    return mesh().time().libs();
 }
 
 

src/dynamicMesh/motionSolvers/displacement/codedPoints0/codedPoints0MotionSolver.H

@@ -103,7 +103,7 @@ protected:
 
     // Protected Member Functions
 
-        //- Get the loaded dynamic libraries
+        //- Mutable access to the loaded dynamic libraries
         virtual dlLibraryTable& libs() const;
 
         //- Adapt the context for the current object

src/dynamicMesh/motionSolvers/displacement/displacement/displacementMotionSolver.C

@@ -94,7 +94,7 @@ Foam::displacementMotionSolver::New
 {
     Info<< "Selecting motion solver: " << solverTypeName << endl;
 
-    const_cast<Time&>(mesh.time()).libs().open
+    mesh.time().libs().open
     (
         solverDict,
         "motionSolverLibs",

src/dynamicMesh/motionSolvers/motionSolver/motionSolver.C

@@ -116,7 +116,7 @@ Foam::autoPtr<Foam::motionSolver> Foam::motionSolver::New
 
     Info<< "Selecting motion solver: " << solverName << nl;
 
-    const_cast<Time&>(mesh.time()).libs().open
+    mesh.time().libs().open
     (
         solverDict,
         "motionSolverLibs",