[IMP] industry_lawyer: add invoice splitting and approval mail workflow

[mega-odoo]

Split sale order invoices per the customer's claimant.
If a customer has multiple claimants, generate one invoice per claimant
and cancel the original invoice.

Implement a submit-for-approval workflow for sending sale quotations, leads
and invoices with attachments.

Only users belonging to a higher access group than the current user
can be suggested as approval users during the sale order or invoice sending in
approval by the field.

When a user submits a sale order or invoice
for approval, the approval user, and currenct user can see this mail via the
'approval app' to track and approve mail.

Also, add an ability to approve and send multiple emails at once via the
'approval app'.

Add a setting in the approval app, make every mail go for submission
for approval before sending.

Task id - 9285

[robodoo]