Refactor ADVANCED_COMPONENT_TYPES

    Modified to a setting in CMS common.py and aws.py
    Also factored out are: SPLIT_TEST_COMPONENT_TYPE,
                           OPEN_ENDED_COMPONENT_TYPES,
                           NOTE_COMPONENT_TYPES,
                           ADVANCED_PROBLEM_TYPES

    This enables third parties to add XBlocks to their system
    without having to make a code change.