3-way matching and bill control are closely related and were very shorts docs,
so in order to make more sense, both docs were merged. Both also had to be updated
for v14 since Odoo behaviour changed: when the bill control policy is set to
'on received quantities' you cannot create a bill anymore unless you have received
at least some products. Previously, you could create a bill for "0" and the "should
be paid' status was set to 'no'. Info about the "Bill status" field was also added
as it is also closely related.
Both blanket orders and calls for tenders shared a good chunk of information
(namely, enabling the feature and purchase agreements types configuration), and,
at the same time, aren't complex enough feature to have their own page, so this
commit merged-s both pages under a new folder "manage deals" where another commit
will add 3-way matching later on. At the same time, some of the content had to be
updated for v14 and it was necessary to provide slightly more in-depth information
across the board.
