Sdoc (#5434)

* [sdoc file view] added file view, history/trash file view for 'sdoc'

* [sdoc file view] sdoc-editor: upgraded it to the latest version(0.1.5)

- sdoc file view: enable 'auto save'
- sdoc shared/history/trash file view: use the read-only sdoc viewer

* [sdoc file view] fixup

frontend/src/utils/constants.js

@@ -1,3 +1,8 @@
+export const defaultContentForSDoc = {
+  version: 0,
+  children: [{id: 'aaaa', type: 'paragraph', children: [{ text: '' }]}]
+};
+
 export const dirPath = '/';
 export const gettext = window.gettext;