MDL-40313 questionbank: Add question filtering API
Add new API for filtering questions, refactoring the options to display old questions
and include subcategories into new question_bank_search_condition classes.
Make the new API pluggable via local_[pluginname]_get_question_bank_search_conditions.
Merge branch 'master' of github.com:MorrisR2/moodle

Conflicts:
	mod/quiz/editlib.php
	question/editlib.php