Misc cleanup and fix flow types

frontend/src/metabase-lib/lib/MultiQuery.js

frontend/src/metabase-lib/lib/NativeQuery.js

frontend/src/metabase-lib/lib/Query.js

frontend/src/metabase-lib/lib/Question.js

frontend/src/metabase-lib/lib/StructuredQuery.js

frontend/src/metabase-lib/lib/StructuredQuery.spec.js

frontend/src/metabase/meta/types/Query.js

frontend/src/metabase/query_builder/actions.js

...src/metabase/query_builder/components/ExtendedOptions.jsx

frontend/src/metabase/query_builder/components/FieldList.jsx

.../src/metabase/query_builder/components/GuiQueryEditor.jsx

...nd/src/metabase/query_builder/components/MetricWidget.jsx

...nd/src/metabase/query_builder/containers/QueryBuilder.jsx