Rich Text feature deprecation bug

@Phil_Seeman is correct, the end date is when we completely shut off access to the old behavior. We change the default behavior on the activation date, in the middle of the migration period, so that developers who are caught off-guard have time to react and fix their apps.

If we waited until the end of the migration period to change the default, developers that are caught off-guard cannot apply the Asana-Disable header patch while they adapt to the change—their app would be broken until they could fully understand and implement the new requirements, which for some upcoming changes could take several weeks.

The API does throw an exception in this case. It will throw the following 400 Bad Request error:

$ curl -X POST -i \
>   https://app.asana.com/api/1.0/tasks \
>   -H 'Content-Type: application/json' \
>   -H 'Authorization: Bearer [redacted]' \
>   -d '{
>   "data": {
>     "html_notes": "text",
>     "assignee": "me",
>     "workspace": <workspace_id>
>   }
> }'

HTTP/1.1 400 Bad Request
...
{
  "errors": [
    {
      "error": "html_lacks_body",
      "message": "Rich text should be wrapped in <body> tag.",
      "help": "For more information on API status codes and how to handle them, read the docs on errors: https://asana.com/developers/documentation/getting-started/errors"
    }
  ]
}