Mesh: modernize C++11

* remove redundant void-arg
* use nullptr
* replace deprecated headers

src/Mod/Mesh/App/FeatureMeshImport.cpp

@@ -39,19 +39,19 @@ using namespace MeshCore;
 PROPERTY_SOURCE(Mesh::Import, Mesh::Feature)
 
 
-Mesh::Import::Import(void)
+Mesh::Import::Import()
 {
     ADD_PROPERTY(FileName,(""));
 }
 
-short Mesh::Import::mustExecute(void) const
+short Mesh::Import::mustExecute() const
 {
     if (FileName.isTouched())
         return 1;
     return 0;
 }
 
-App::DocumentObjectExecReturn *Mesh::Import::execute(void)
+App::DocumentObjectExecReturn *Mesh::Import::execute()
 {
     std::unique_ptr<MeshObject> apcKernel(new MeshObject());
     apcKernel->load(FileName.getValue());