* Made OuputPage::showPermissionsErrorPage() show a different messages for 'read...

* Made OuputPage::showPermissionsErrorPage() show a different messages for 'read', 'edit', 'create' and 'upload' actions to saying "You need to log in to do this action" when 1) The user is not logged in 2) The only error is a permissions error (no block or something else) and 3) The error can simply be avoided by logging in
* This replaces OuputPage::loginToUse() functionnality, made it simply throw a PermissionsEror exception and updated all calls in core
* Same for the check in SpecialUpload::execute(), EditPage::userNotLoggedInPage() and EditPage::noCreatePermission()
* Throw the same exception in EditPage::attemptSave() whether the user is logged in or not and let OuputPage::showPermissionsErrorPage() decide which message to display
* Replaced call to deprecated OutputPage::blockedPage() in SpecialUpload
* Displayed messages are the same as now, except the title is always "loginreqtitle"
* 'nocreatetitle' and 'uploadnologin' messages are still used by extensions, so I kept them, but the message 'whitelistedittitle' is not used anymore and has been removed