Global CLI installation should not be required for unpack

[spalladino]

Since unpack requires an empty directory, the oz binary cannot be installed locally and run via npx oz unpack - it must be installed globally. Even worse, the CLI is then immediately installed locally as it's part of the starter kit dev dependencies.

Reevaluate the unpack flow to ensure the CLI can be installed locally. Some options that come to mind are:

• Run unpack from outside the CLI, potentially in a package that follows the create- convention to use npm init (see #44)
• Allow the local directory to have a package.json, and just add the kit's dependencies to it

[frangio]

Using npm init would be the best IMO.