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 
This creates a requirement that non-admin users must have a role == their scope name to publish. Obviously registry-frontdoor won't care about this because isAdmin(true) but we have no mechanism to introduce scopes into _users so it seems weirdly superfluous. Are we going to provide a mechanism for people running their own couchapp to do this, or leave it as an exercise?