Plugin generator should support creating scoped packages

[phillipskevin]

Using a scoped package name when creating a plugin like:

? Project name @phillipskevin/scoped-package

creates a package with

"name": "phillipskevin-scoped-package",
...
"repository": {
    "type": "git",
    "url": "git://github.com/phillipskevin/phillipskevin-scoped-package.git"
},
...
"main": "dist/cjs/phillipskevin-scoped-package"
...
"steal": {
    "main": "phillipskevin-scoped-package",
}

[phillipskevin]

when using scoped packages, the generator should also add --access=public for publish scripts (perhaps optionally).