Include lower bound in MaxSize[N] predicate

[fthomas]

In #455 (comment) @matthedude noticed that the type MaxSize[N] = Size[LessEqual[N]] predicate should include a lower bound like this type MaxSize[N] = Size[NonNegative And LessEqual[N]]. In case of the Arbitrary instance for collections with any Size[P], this would give as a correct Arbitrary[Int Refined P] for the size of such collection that does not generate negative values when Size[P] is MaxSize[N].

I agree that we should do this.