Add CSRF check on login and logout
This is a minor issue and not worth a backport in my opinion as it could break more things than it's worth having it.
 Redirect to index if the logout link is accessed without valid session

This is needed to prevent "Token expired" messages while login if a session is expired
@see https://github.com/owncloud/core/pull/8443#issuecomment-42425583
Merge branch 'master' into csrf-on-login-and-logout

Conflicts:
	core/templates/login.php
Merge pull request #8443 from owncloud/csrf-on-login-and-logout

Add CSRF check on login and logout