Support packages from non-Loupeteam organizations

[AndrewMusser]

Currently, LPM makes a number of hard-coded assumptions about packages belonging to the @loupeteam organization. We would like to support users bringing their own package registry, with their own packages, and for LPM to be able to manage those as well. This would touch all of the following:

• LPM login process would have support for logging in to an explicit privately scoped registry.
• Packages that have an explicit scope called out (i.e. @andrew/my_package) would not have the @loupeteam scope pre-pended internally.