New scope name for full access

This changes the scope for requesting full storage access to '*' as discussed in remotestorage/spec/issues/48.

When an app requests full access, the appropriate scope parameter is sent to the storage provider, based on the spec version the provider supports. E.g. for storage servers supporting a spec prior to -02, the parameter is still 'root'.

This PR should only be merged for the 0.9 release, as the change of the scope is a breaking change.