Modify the interpolation tasks to do it by 'n' nodes

[fabricix]

Introduction

Currently the interpolation tasks are performed over two nodes of a 1D element.

Objective

In order to expand the code to 2D or 3D, these operations must be carried out in a more general way, using a loop over all nodes in the element.

Verification

As an initial verification, the solution given by the implementation must be coincident with the current implementation, that does the loop only over two nodes.