Add sample project for upgradeable proxy usage

[zoeyTM]

resolves #641

[jkirkpatrick]

OZ upgradable contracts should not accept constructor parameters... How should I pass parameters when using a custom initializer? How do you specify the initializer or upgrade functions, e.g. updateToAndCall?

[zoeyTM]

@kanej merging because it's already rebased and it doesn't look like we update the versions of the example projects. We can update them later all at once if we want.

I also tried adding the ENS project to the workspace, but it's still bugged. I briefly tried to fix it, but it seems like a much more involved dive is needed and it's not worth the time right now.