NEW EXAMPLE: Saving Related Model Data (HABTM)

Added a new example to the Saving Related Model Data (HABTM) section to help clarify the correct array formatting for HABTM when passing more than one associated id.
Merge pull request #1837 from justinatack/patch-1

NEW EXAMPLE: Saving Related Model Data (HABTM)
[fr] follow #1837

- add french translation
- fix doc example format
[zh_CN] done /zh/controllers/request-response.rst
[zh_CN] fix error: ``AppHelper` -> ``AppHelper``
Merge pull request #1839 from blackpuppy/zh

[zh_CN] done /zh/controllers/request-response.rst