[Integration] Changed the position of the if condition to prevent the function building a unnecessary graph and shortened the custom node execution function by assuming that input0 is always v and input1 are always thresholds

[Integration] Interface of execute_custom_node.py to onnx_exec.py finished and first draft of unit test added

[Test] Created new test for multi-thresholding, now with input shape (6,3,2,2) and threshold shape (3,7)

[Exec] Changed multi-thresholding to handel right input shapes and [Test] Deleted old multi-thresholding test