Normalize tuple interfaces eliminating the separate interface for RightTuples

The current split of tuples into LeftTuples and RightTuples adds complexity to the system and makes impossible for the system to join (concatenate) 2 left tuples.

The goal of this task is to normalize all tuple interfaces into a single interface, allowing two-input nodes like joins to join 2 tuples, independently of the number of elements in each.