Feature #4843 : blocking the download of file attachments attached to publications

- upgrading the access control mechanism to take in account the context in which the access is verified
- upgrading the document exporting in order to not include document forbidden to download
- upgrading the display of attachment according to the new forbidden download information
- refactoring some code

Don't forget to check :
- https://github.com/Silverpeas/Silverpeas-setup/pull/13
- https://github.com/Silverpeas/Silverpeas-Core/pull/459