[FIX] website_quote: enable translation for signature modal

Adding <span>'s inside the <p> will allow the translation editor to
distribute the right branding on the strings to be translated.
[IMP] project: select project pricelist based on customer pricelist

Add an invisible field `pricelist_id` to project.project form view, so that when
`partner_id` is changed, `onchange_partner_id` method can also set the
pricelist properly (previously, the pricelist was not set because the
field was not in the view).