Feature/edit metadata authorization

I assume that pds_handle contain user group name(s) and thus we don't need to add roles. To reflect this I added customized method "groups" to user model. If the assumption is incorrect I will fix it and edit roles file.

@ekate So just as a follow up you probably want just `read_groups` since that covers read and discover permissions. Also if we decide that all created files should be readable by everyone I would like to set the group permissions in an `after_create` block in the nyucore model to keep the controller cleaner.