Description
This pull request adds three classes that can be used to create the lattice of the non redundant set of elements of another lattice's domain. These classes provides the methods necessary for the definition of the classical operations on elements of a lattice (such as lub, glb, widening, narrowing, less or equal). These methods includes a method that given a set create an equivalent set that is not redundant, an extrapolation heuristic that is used for the definiton of the widening operator, an Egli-Milner less or equal relation method and an Egli-Milner connector method that given two sets it yields a new set that is in the Egli-Milner less or equal relation with the two.
The pull request also adds the NonRedundantPowersetOfInterval which defines a non relational value abstract domain whose domain is all the sets of non redundant sets on intervals.

Implemented features
this pull request adds 4 classes:

• NonRedundantPowerset: it generalizes the concept of non redundant powerset of the domain of a lattice (this lattice can be both relation or non-relational).
• ValueNonRedundantPowerset: it is a NonRedundantPowerset, but only accepts ValueDomain an ValueExpressions.
• NonRedundantPowersetOfBaseNonRelationalValueDomain: this class is specific for BaseNonRelationalValueDomain.
• NonRedundantPowersetOfInterval

Further content
This pull request follows this paper: https://www.cs.unipr.it/Publications/PDF/Q349.pdf