Make google drive client secret and dropbox api secret a password field

Fix issue #5794

apps/files_external/lib/config.php

@@ -61,7 +61,7 @@ class OC_Mount_Config {
 			'configuration' => array(
 				'configured' => '#configured',
 				'app_key' => 'App key',
-				'app_secret' => 'App secret',
+				'app_secret' => '*App secret',
 				'token' => '#token',
 				'token_secret' => '#token_secret'),
 				'custom' => 'dropbox');
@@ -80,7 +80,7 @@ class OC_Mount_Config {
 			'configuration' => array(
 				'configured' => '#configured',
 				'client_id' => 'Client ID',
-				'client_secret' => 'Client secret',
+				'client_secret' => '*Client secret',
 				'token' => '#token'),
 				'custom' => 'google');