[RFC] Transferring to JuliaGraphics organization

[kimikage]

It's not a big deal that this package is in a personal repository, but I'm a little concerned about its lack of popularity. 😭

I still have some plans for changing this package, but I don't think we have a problem committing them under the organization. Rather, I think the problem is the dependency chain in the JuliaImages ecosystem. For now, this package is "isolated", though.

Although the transferring to organization is not an urgent issue, I think it's one to consider if we want to reorganize the repositories of ColorTypes, Colors and ColorVectorSpace.

cc: @timholy, @johnnychen94