Update Welcome message to remove mentions of DM

When a new project is create, we display a welcome message that explains we imported the DM package. We should update it since DM doesn't exist anymore.

Your project was initialized by importing the Nuxeo DM default configuration Application Template, that declares the main objects used by the Nuxeo Platform (such as File document type, default life cycle, Folder, etc.) so that you just have to modify them to see the result.
You can unimport this template by going to the Application Template library: Settings And Versionning > Application Templates > Nuxeo DM Default Configuration > Remove.