Convert drag-drop into text question type JS from YUI to AMD

This question should work almost exactly the same way it worked before, and the automated tests are a pretty good test of the functionality. The main thing that needs to be tested manually are visual display issues, and that the question types works on the full range of browsers and devices. For manual testing instructions, see MDLQA-8183 , which is the standard QA test for this question type. Also the docs: https://docs.moodle.org/35/en/Drag_and_drop_into_text_question_type The only change from the previous behaviour is that when a drag item needs to me moved to a new place (e.g. if you drag something into a place that is already full, and the thing that was there needs to be sent home, then that item is moved smoothly, rather than just jumping to its destination. This also applies when answering the question using only the keyboard (tab to hilight a place, then use left-right arrows).