Tend to use std::array instead of raw array in `Element` namespace

[juliolopeztorres]

Current use, example Quadrilateral4.h:

    const Coordinate::Coordinate<T,3>* v_[4];

Preferred usage:

    std::array<const Coordinate::Coordinate<T,3>*, 8> v_;

[juliolopeztorres]

Check the typing at constructor level, if possible.

    Hexahedron8(const Id id,
                const Coordinate::Coordinate<T,3>* v[8],
		const Layer* lay,
                const Model* mat = nullptr);