ENH: Added flag to help debug Attribute::isValid

If the flag is true the method  will print the invalid items or teh invalid status of
its associations to std::cerr.
Status Job ID Name Coverage
  External
passed cdash

failed ghostflow-branch-check-master

failed ghostflow-commit-check

pending smtk@master-junction-osx-shared-release+remus
failed smtk@master-kerbin-windows-shared-release+cgm+remus

00:07:03

failed smtk@master-moho-linux-shared-relwithdebinfo+cgm+python3+remus+vtk

00:04:18

failed smtk@master-moho-linux-shared-relwithdebinfo+cgm+remus

00:07:42

failed smtk@master-moho-linux-shared-relwithdebinfo+cgm+remus+vtk

00:05:59

failed smtk@master-praxis-windows-shared-release

00:11:41

failed smtk@master-talosiv-osx-shared-release+cgm+matplotlib

00:37:52