[IMP] rental: added saas-19.1 updates

[fw-bot]

Included the following updates from the 19.1 update:

• Product card changes
• Sales tab: Contains the rental period (Periodicity) now under the Rental section. 
• One periodicity per product, with pricelists if you want to set different prices (no rental prices rules anymore)
• The Configuration menu will not have Rental Periods
• Settings page layout has changed
• Sales Price is for the base rental rate
• The Prices tab is for other rental rates
• Request Signature: For two signatures, if one signature is the user, then there is a Sign Now option. The to and from fields are automatically lifted from the template document.
• Will need new screenshots for any product card and setting pages.
• No more Duration field on Rental Order, updates prices link changed location.

Task: https://www.odoo.com/odoo/action-4043/5454313

Forward-Port-Of: #15998

[robodoo]

[fw-bot]

@meval1006 this PR targets master and is the last of the forward-port chain.

To merge the full chain, use

@robodoo r+

More info at https://github.com/odoo/odoo/wiki/Mergebot#forward-port