Scoped modules

Partly a proof-of-concept of scoped modules in the couchapp registry for the purposes of dogfooding/bootstrapping, but more importantly, updates to the vdu so that users don't accidentally *depend on* scoped modules from existing global packages.

Review at your liesure: @seldo @othiym23 @iarna 
We're leaving it as an exercise for the user for now.

Recall: we used this earlier in 2014 to see what had to change in the npm client to support `@org/foo` syntax, by giving it something to bang on.  (By the time @othiym23 started implementing scopes, we had a mostly-functional npmE to play with, so this never ended up being al THAT relevant.)