Refactoring: generalized BoundaryTags to EntityTags

src/TNL/Meshes/DefaultConfig.h

src/TNL/Meshes/Mesh.h

src/TNL/Meshes/Mesh.hpp

...NL/Meshes/MeshDetails/layers/EntityTags/ConfigValidator.h

src/TNL/Meshes/MeshDetails/layers/EntityTags/Initializer.h

src/TNL/Meshes/MeshDetails/layers/EntityTags/Layer.h

src/TNL/Meshes/MeshDetails/layers/EntityTags/LayerFamily.h

src/TNL/Meshes/MeshDetails/layers/EntityTags/Traits.h

src/TNL/Meshes/MeshDetails/traits/MeshTraits.h

src/TNL/Meshes/MeshEntity.h

src/TNL/Meshes/MeshEntity.hpp

src/Tools/tnl-decompose-mesh.cpp

src/Tools/tnl-mesh-converter.cpp

src/UnitTests/Meshes/CMakeLists.txt

src/UnitTests/Meshes/EntityTagsTest.cpp

src/UnitTests/Meshes/EntityTagsTest.h