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 Ok I see what's happening. You can authorize on the ID in hydra because that's how they define their default permissions. It's ID and not object based because the ID is always a solr document id.

So for Hydra permissions to work properly you want to authorize on the document id, like you're doing it:

```ruby
    authorize! :show, params[:id]
    @book = Book.find(params[:id])
```

If you instead loaded the object into the ivar first and authorized against the object (or used `load_and_authorize_resource` which does that automagically) such as:

```ruby
    @book = Book.find(params[:id])
    authorize! :show, @book
```

Then there would have to be new matching permissions in the ability.rb file in the form: `can :something, Book`

So that definitely looks good.