Also add a few comments to note understanding of code

rco notes that group tests are generally intersections, if the user has *any*
group set on the object he can see/use it. This change is a literal
translation of the original semantics, which may be wrong.

just forwarding the context object does not count as using it, if callees want
a context they can ensure they've got one on their own

[IMP] don't pointlessly recreate view_obj every time _views_get is called, better use of pool & data APIs

* Deleted: manually translation in es.po

This checkbox caused greate confusion, as it was doubled in the tax form view. Field is already present in line 937

Thanks for merging.

* document_page should have disappeared a long time ago, no idea why it
  remains
* thunderbird seems to have suffered from odd conflictual moves (or lack
  thereof)
* audittrail was removed but not deactivated in rosetta

[FIX] website:  ir_http: when rerouting url containing default language -> url without language, the ? was missing, leading to wrong urls.

[FIX] website: define languages variable outside of an 'if' as it is used below in the same template, leading to a crash due to the variable not always being defined.

Fixed checkout redirection that was meant to clean the session (incorrect sale order or transaction) that may happen
when having issues with the payment.

add the possibility to users to follow a forum and be automatically followers of new
questions, using some new subtypes on the forum.forum model that do the auto subscription.

Also added a profile link on the forum, when logged.

Also added a subscribe button on the forum.

Added translation of the message
Now this style of message in a CSS class and not use HTML tags

Now when a search is conducted in the fields and not m2o results have a message saying "No results to show" since the show nothing will display the user is confused

[FIX] remove closing reason 'an answer was accepted', the questions should be left as open to be possible to improve the answer afterward