Add fallback to two-letter locale for Swedish

As it is already done for French and Spanish, please add the fallback to two-letter locale for Swedish

Currently, there is a translation file for "sv-SE" with messages-sv-SE.json => there must be a fallback for "sv" in src/main/resources/OSGI-INF/deployment-fragment.xml

     <copy from="nuxeo.war/ui/i18n/messages-sv-SE.json"
          to="nuxeo.war/ui/i18n/messages-sv.json" />