[FIX] web_calendar: Revert d9e6a7a as was fixed differently at rev e220136

Fixing calendar view errors, opw 609989
[FIX] l10n_lu: taxes (amont/aval)

The accounts "TVA en amont" were not used by the l10n_lu chart of accounts.

Instead the accounts "TVA en aval" were used for all taxes both sale and purchase taxes.

(Manual rebase of PR #735)
[FIX] l10n_lu: wrong mapping of accounts to P&L financial report

Account 655 and its child 6554 were both mapped.
Fixed by unmapping 655 and mapping all its direct children.

(Manual rebase of PR #733)
[FIX] tools: mail: fixed last commit, solving an issue with the html2plaintext introduced another issue with notes. Reverting to the first version.
[FIX] project: default_groups_ref expects the format module.xml_id (opw 610098)
[MERGE] forward port of branch 7.0 up to 7a928b1
[MERGE] forward port of branch saas-3 up to 24484c8
[FIX] website_forum: fixed controller creating a new forum tha was crashing.
[FIX] website_forum: fixed issue when voting. The method should work in batch. Previously to this implementation having one post with a vote bypassed the other posts without vote when called with several ids.