Retire DrakeVisualizer.jl

[rdeits]

I think it's time for DrakeVisualizer.jl to retire. I haven't used it in years, and I don't think anyone else has either.

To make sure it has a happy retirement, I've gone and created Project and Manifest files for the package itself and for its demo notebook. That should ensure that they remain usable forever, even if the package isn't getting any new features.

@tkoolen any objections to putting this package out to pasture?

[tkoolen]

Retiring the package sounds good to me.