Fix rule-of-3 for the Tensor module.

Adds copy constructors to Tensor ops, inherits assignment operators from
`TensorBase`.

Addresses #1863
diff --git a/unsupported/Eigen/CXX11/src/Tensor/Tensor.h b/unsupported/Eigen/CXX11/src/Tensor/Tensor.h
index 17cee49..200f58b 100644
--- a/unsupported/Eigen/CXX11/src/Tensor/Tensor.h
+++ b/unsupported/Eigen/CXX11/src/Tensor/Tensor.h
@@ -388,6 +388,7 @@
       resize(TensorEvaluator<const Assign, DefaultDevice>(assign, DefaultDevice()).dimensions());
       internal::TensorExecutor<const Assign, DefaultDevice>::run(assign, DefaultDevice());
     }
+
     template<typename OtherDerived>
     EIGEN_DEVICE_FUNC
     EIGEN_STRONG_INLINE Tensor(const TensorBase<OtherDerived, WriteAccessors>& other)