function registerOp(name, opFunc) {
	  var opMapper = {
	    tfOpName: name,
	    category: 'custom',
	    inputs: [],
	    attrs: [],
	    customExecutor: opFunc
	  };
	  CUSTOM_OPS[name] = opMapper;
	}
Register an Op for graph model executor. This allow you to register
TensorFlow custom op or override existing op.

Here is an example of registering a new MatMul Op.
```js
const customMatmul = (node) =>
   tf.matMul(
       node.inputs[0], node.inputs[1],
       node.attrs['transpose_a'], node.attrs['transpose_b']);

tf.registerOp('MatMul', customMatmul);
```
The inputs and attrs of the node object is based on the TensorFlow op
registry.

@param name The Tensorflow Op name.
@param opFunc An op function which is called with the current graph node
during execution and needs to return a tensor or a list of tensors. The node
has the following attributes:
   - attr: A map from attribute name to its value
   - inputs: A list of input tensors

@doc {heading: 'Models', subheading: 'Op Registry'}