AuthManager: Always whitelist some special pages

AuthManager: Always whitelist some special pages

Special:UserLogout should be whitelisted, if Special:UserLogin is whitelisted,
as otherwise the user is able to login, but not able to logout anymore (given,
that the sys-admin hasn't change the $wgWhitelistRead config variable).

Special:ChangePassword redirects to Special:ChangeCredentials. Instead of
adding this special page, it should be done explicitly in the
wiki configuration (LocalSettings.php). For this reason, the whitelist is
removed, too.

Change-Id: I271efb517bf0ec0022e6fe29673570ca08e8fe1a