Add more methods for scale

[schillic]

julia> methods(scale)
# 3 methods for generic function "scale":
[1] scale(α::Real, x::Interval) in LazySets at .julia/dev/LazySets/src/Sets/Interval.jl:587
[2] scale(α::Real, Z::Zonotope) in LazySets at .julia/dev/LazySets/src/Sets/Zonotope.jl:303
[3] scale(α::Number, pz::PolynomialZonotope) in LazySets at .julia/dev/LazySets/src/Sets/PolynomialZonotope.jl:217

Sets for which scaling is easy (maybe the others are also easy :man_shrugging:):

• [ ] AbstractZonotope (generalize existing method)
• [ ] EmptySet/ZeroSet (identity)
• [ ] Universe (identity except for 0 → ZeroSet)
• [ ] Singleton
• [ ] LineSegment
• [ ] Ball*
• [ ] Hyperrectangle
• [ ] VPolytope/VPolygon
• [ ] HPolytope/HPolygon (using vrep > scale > hrep)