Arrabiata: implement a gadget to perform elliptic curve scaling using "next row"

[dannywillems]

At the moment, there is a gadget called ECScaling performing the scaling of an elliptic curve point in 255 rows, and rely on methods called "save/load".
However, these methods save/load are also used to access a value located at the previous row.
A gadget could be saving the next point on the next row intsead of using the permutation argument.

The permutation argument is used later to fetch the points and the random scalar. We do suppose the permutation argument exists at the moment.

An elliptic curve scaling gadget can be optimised to do more than one "double-and-add" operation per row if we do have 17 columns and the next row accessible. We leave this for the future.