Add example comaparing the results found for 2DEG Chris geometry when using Fenics vs poisson package

Merge branch 'feature/refactor_org_2' of ssh://gitlab.kwant-project.org:443/asantosnet/Poisson_Solver into feature/refactor_org_2

Added __all__, added imports in __init__, fixed InHull (missing self.points_coordinates = self.generate_points()), changed name of PointsShape to Deulaynay, changed Geometry to ContinuousGeometry and other minor changes