R1:e7f94d7528eb

Properly version Legalpad documents

Summary: Fixes T12933. This now creates a new DocumentBody when creating or editing a legalpad document.

Test Plan:
Create a new document, edit document. Check database that version is saved as new row, and timestamps are correct.

```mysql> select * from legalpad_documentbody;
+----+--------------------------------+--------------------------------+--------------------------------+---------+---------------+--------+-------------+--------------+
| id | phid…