[FIX] crm: fixed bug in m2m between sales teams and stages introduced
when cleaning the models. The m2m table name is different when defined
in sales_team or in stages, leading to a quie strange behavior.
[FIX] website_forum: fix broken forum activation email due to the migration to the new API.

Next step: write tests. Hooray.
[FIX] hr_holidays: fix virtual remaining leaves computation.

Now only validated allocation requests are taken into account
when computing the number of virtual remaining leaves (leaves
+ pending leaves). This avoid creating allocation request to
have virtual remaining leaves artificially added.
[IMP] mass_mailing: add creation date in fields
to display it on list view + perform search on it.
[IMP] crm: added reason for loosing opportunities
[IMP] sale & sale_stock : removed 'Enable Invoicing Sales order lines' group from user setting and 'Generate invoices based on the sales order lines' group from sale setting.
[ADD] added website countdown snippet