[FIX] crm: avoid constraint errors when merging partners

As for the _update_foreign_keys, the _update_reference_fields method may raise an unique constraint when merging two partners.
In such case, the new record is not relevant and can be removed.
[IMP] website_forum: performance improvements

- avoid to browse on every question/answer, only the 20 most recent ones (need to manually update the view to see the real number of q&a)
- do not render hidden tabs (leakage of information and useless rendering)
- add related fields to speed up vote search (need to be stored to be efficient)
[FIX] website_forum_doc: default stage for post + removed unused import + added toc_id field in post tree view
[FIX] im_chat : forget part of sql request, and fix ambiguous column name
[IMP] survey: display sum for numerical answers
[FIX] website_forum_doc: fixed last commit, wrong branch pushed (missing code review)
[FIX] Website_gengo: check API key with SUPERUSER_ID since private_key is really private
[FIX] Website translation pairing bug

I think we could get rid of the .trim() calls (for performance sake)
but I don't want to break anything so I'll leave them.
[FIX] pad: fullscreen pad behind the top nav bar