Support scoped packages

[nexdrew]

Packages with scoped names (e.g. @scope/pkg) need to have the slash URL-encoded (e.g. @scope%2Fpkg), for any package name given to ls() or any dependencies encountered. Otherwise, the Couch registry returns 404.

This currently blocks the ability to manually add a scoped package to the whitelist in npm Enterprise (called via package-whitelist).

npme add-package @kadira/storybook
analyzing dependencies for @kadira/storybook:
Cannot convert undefined or null to object
[]
[?] add dependencies to /etc/npme/data/whitelist? (Y/n)

could not load @kadira/storybook@* status = 404