Fixes #436

This uses class template specialization to avoid ever calling AABB with conflicting template params (e.g., MatrixX3D and DIM=2). The old code was all dynamic so it lead to conflicting compilation paths.

I claim this is a reasonable C++11 solution. If we were using C++17 then we could use if constexpr which would be significantly less code and more readable.

Unless I notice something broken with this, I'll also fix the nasty dynamic situation in signed_distance similarly. And then we can add [to AABB] a

static_assert(DerivedV::ColsAtCompileTime == DIM || DerivedV::ColsAtCompileTime == Eigen::Dynamic,"V's #columns must either match DIM or be Dynamic.");

So that bogus compilation paths get caught.