show link to clear plaintext email account passwords if enabled; set store-plaintext-passwords default to 'off'; fixes #557

Signed-off-by: Michael Kaufmann <d00p@froxlor.org>

lib/navigation/00.froxlor.main.php

@@ -272,6 +272,12 @@ return array(
 					'label' => $lng['admin']['autoupdate'],
 					'required_resources' => 'change_serversettings',
 					'show_element' => extension_loaded('zip')
+				),
+				array(
+					'url' => 'admin_settings.php?page=wipecleartextmailpws',
+					'label' => $lng['admin']['wipecleartextmailpwd'],
+					'required_resources' => 'change_serversettings',
+					'show_element' => (Settings::Get('system.mailpwcleartext') == true)
 				)
 			)
 		),