Support for unplugged keyword in .script files.

User progress can now show unplugged level(s) in same stage as other levels.  That view remains compatible with legacy approach which is that stages with a single level have them listed as unplugged.
hm, I think there have been changes to this code... in particular we're not using the admin_script local anymore. did you get a merge conflict?

Current code looks like this:

````
              - if current_user.try(:admin?)
                - if can? :edit, sl.level
                  = link_to(t('crud.edit'), edit_level_path(sl.level), style: 'display: block; width: 30px;', title: sl.level.name)
                - else
                  %span{style: 'display: block; width: 30px;'} &nbsp;
````