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

Added module in Geometry to plot the geometry as well as a function in plot_toolbox.py to plot a Geometry instance. Added 3D plotting of System, Geometry, Mesh and of a set of points with mayavi

Changed how InHull works. By default it will calculate the points with generate_points when the isntance is initialized. Whenever a translate or rotate is called the self.points_coordinates will change. Also added get_bbox to shapes. Fixed a bug in geometry_toolbox and mesher. Added visual  tests in shapes.py

SysEquations.solver by default does not initialize another instance of Solver. It does the latter in case new_instance is True, self.solver != solver or self;solver_instance is None.