Rebuild the way modals are constructed to support nesting.

cms/djangoapps/contentstore/features/common.py

...ontentstore/features/component_settings_editor_helpers.py

...jangoapps/contentstore/features/discussion-editor.feature

cms/djangoapps/contentstore/features/discussion-editor.py

cms/djangoapps/contentstore/features/video-editor.py

cms/static/coffee/spec/views/module_edit_spec.coffee

cms/static/coffee/spec/views/upload_spec.coffee

cms/static/js/spec/utils/drag_and_drop_spec.js

cms/static/js/spec/views/modals/base_modal_spec.js

cms/static/js/spec/views/modals/edit_xblock_spec.js

cms/static/js/spec/views/xblock_container_spec.js

cms/static/js/spec/views/xblock_editor_spec.js

cms/static/js/spec_helpers/edit_helpers.js

cms/static/js/spec_helpers/modal_helpers.js

cms/static/js/views/edit_chapter.js

cms/static/js/views/modals/base_modal.js

cms/static/js/views/modals/edit_xblock.js

cms/static/js/views/settings/main.js

cms/static/js/views/uploads.js

cms/static/js/views/video/translations_editor.js