It's not possible to delete the default instance of the blog app

Steps to reproduce :

• On a new instance, install the Blog application
• Go in Others -> Blog in the admin
• Click on "Delete" next to the only blog instance

This "Delete" leads the user to the deletion page of the whole blog space, which includes the applicative code + the contents of the default blog. Depending on the user profile, the following will happen :

• If the user is marked as "advanced", he will get a warning asking to confirm that he wants to delete the classes of the blog app, which is not what the user expects at first
• If the user is not marked as "advanced", the deletion will be canceled with the following message :