MDL-58707 mod_assign: Fix param type for returned field

The ‘description’ field is populated via a get_string call, this means
that it may content html.
The component used for translation is also fixed in this commit.

mod/assign/externallib.php

@@ -818,7 +818,7 @@ class mod_assign_external extends external_api {
                     new external_single_structure(
                         array(
                             'name' => new external_value(PARAM_TEXT, 'field name'),
-                            'description' => new external_value(PARAM_TEXT, 'field description'),
+                            'description' => new external_value(PARAM_RAW, 'field description'),
                             'text' => new external_value (PARAM_RAW, 'field value'),
                             'format' => new external_format_value ('text')
                         )

mod/assign/submission/onlinetext/locallib.php

@@ -291,7 +291,7 @@ class assign_submission_onlinetext extends assign_submission_plugin {
      * @return array An array of field names and descriptions. (name=>description, ...)
      */
     public function get_editor_fields() {
-        return array('onlinetext' => get_string('pluginname', 'assignsubmission_comments'));
+        return array('onlinetext' => get_string('pluginname', 'assignsubmission_onlinetext'));
     }
 
     /**