First step towards template models : selection UI in the back-office and
storage of the model property
Introduce the notion of "files settings" that for now precise where
should be stored permanent and temporary files
More TODO
Refactoring of the template resolution
- Try to get template content from tenant folder, then global folder,
  then classpath
- Generate an technical id (hashcode) for each template instead of
  readable id, since it does not have a real meaning
Apply entity model when rendering the front view