[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.
[CLEAN] event: removed unnecessary count_registrations field;
on form view, display attendees (not canceled, ...) instead of
registration count.