Restore Project.toml with updated Pkg uuid and bump version to 0.66.0

[martinholters]

Note: As this bumps the version, the merge commit should also be tagged as a release. I don't see why we shouldn't do so, soon, just want to be clear about it.

[martinholters]

ERROR: Pkg.Types.CommandError("Cannot add package with the same name or uuid as the project")

Travis just continues, but AV fails. I guess the build_script needs some adjustment...

[martinholters]

... or could we make Pkg.clone more tolerant here, given that its raison d'être is to ease transition?

[KristofferC]

Ref travis-ci/travis-build#1392. Could also make Pkg.clone do nothing if it tries to clone the current project.

[martinholters]

Yes, fixing the Travis script is a good idea, of course; too bad we cannot centralize that for AppVeyor. But eventually, people will have to adjust the AV scripts, so forcing them to do so when adding a Project.toml might be ok.

[martinholters]

CI back to all-green 🎉

My plan would be to merge #560 first, then this on top to have a reasonably "deprecation clean" release.

Note: This should be squashed upon merge.