Improve ability of modifying document types labels

When the document type label is the same as another Studio property (e.g. lfecycle state label), there is currently no way to change the displayed value of one entry without changing the display value of the other entry.
E.g. default lifecycle state and document type both named "project".
In messages.*.properties, the entry project=Projet changes both values displayed.

It is specifically requested in https://github.com/nuxeo/nuxeo/blob/master/nuxeo-dm/nuxeo-platform-webapp-core/src/main/java/org/nuxeo/ecm/webapp/contentbrowser/DocumentActionsBean.java#L246 to change messages.get(doc.getType()) in messages.get(doc.getDocumentType().getName())