Merge branch 'move_sortable_list' into 'master'

chore(sortable-list): move code according to standard

See merge request pubsweet/pubsweet!518

packages/components/SortableList/index.js

-module.exports = {
-  client: {
-    components: [() => require('./SortableList')],
-  },
-}

packages/components/SortableList/src/index.js

+import SortableList from './SortableList'
+
+export default SortableList

packages/components/SortableList/SortableList.test.js → packages/components/SortableList/test/SortableList.test.js

@@ -4,8 +4,8 @@ import { mount, shallow } from 'enzyme'
 import { DragDropContext } from 'react-dnd'
 import TestBackend from 'react-dnd-test-backend'
 
-const SortableList = require('./SortableList').default
-const { DecoratedItem } = require('./SortableList')
+import SortableList from '../src'
+import { DecoratedItem } from '../src/SortableList'
 
 function wrapInTestContext(DecoratedComponent) {
   return DragDropContext(TestBackend)(