MDL-38214 Questions: Add MCS, MCVS, MCHS Cloze subquestion types

Daniel Seemuth add MCO,MCVS,MCHS new multianswer subquestion types
qtype_multianswer_initialise_multichoice_subquestion.
Pierre Pichet MCO to MCS, add shuffling display in decode and verify edit_multianswer_form.php
add test_questiontext_extraction.

Signed-off-by: Pierre Pichet <pichet.pierre@uqam.ca>