Git commits in Moodle 3.7.0 by Dani Palou

commit 468ee73bba92669dfb95a99ec52ef429eef135c7
Author: Dani Palou <dani@moodle.com>
Date:   Mon, 04 Feb 2019 21:22:46 +0800
Tag:    v3.7.0-beta

MDL-64761 assign: Add tests for hidden grader in WS

commit 208e1376be51c542aea5bd3376b72026e3ddad2f
Author: Dani Palou <dani@moodle.com>
Date:   Mon, 04 Feb 2019 19:28:34 +0800
Tag:    v3.7.0-beta

MDL-64761 assign: Return grader -1 when hidden in get_submission_status