[IMP] account/sale/sale_layout: standardization of Quotation/Sale Order/Invoice printed layout + add missing information

- Column alignment and order are now uniform across those reports.
- Display Due date on invoices.
- Display payment term and fiscal positions notes.
[IMP] graph view on contacts
[FIX] sell future events only, not old ones
[ADD] website_slides: new module doing stuff. I swear.

Courtesy of a lot of people including Mantavya Gajjar(mga-odoo), Ravi Gadhia(rga-odoo),Vijay Patel(vip-odoo), Pariket Trivedi(ptr-odoo)
[REVIEW] Pre-merge review. This commit will have to
be squashed, but not before the end of the review process.