Bug #5569 - fixing the Web document edition in multilingual behavior

(adding unit tests around webdav repository !! WTF ?!?)
(cleaning unused service methods of WebdavService and adding unit tests around webdav repository...)
(turning the servlet of attachment actions to an Silverpeas authenticated one !!!! WTF ?!?)
(adding service to retrieve which content language is handled in webdav for an attachment)
(adding service to move webdav attachment node from an component instance identifier to another one)
(the preview or view services was not working with content language but with user language)
(fixing some little stuffs around the document copy)
(fixing some little stuffs around the document move)