[FIX] mrp: rounding issues and efficiency replacement

Before, when you would put a quantity in a BoM line that was not rounded
to its UoM (e.g. use 0.3 piece with rounding 1.0) it would not round this
quantity in the MO also (when exploding the BoM), and the user could also
enter a not rounded quantity himself for the quantity produced or
consumed.

The moves were split with the exact quantities, but the moves were validated
taking into account rounded quantities. This resulted in either moving 2
pieces instead of 1 (entering 0.7 or 1 piece) or raising an error telling
you can not process moves with 0 quantity (0.3 piece).

As product_efficiency and product_rounding was removed from the BoM/BoM
line in v10, if the rounding is correctly handled, the feature could work
like in v9, by e.g. putting 1.03 in the bom line (97% efficiency) and
rounding up when exploding the BoM (e.g. producing 10 pieces would put
it to 11).

When "producing", we round the produced qty to the product uom (it does
not make sense to produce 1.32 if your uom rounding is 1.0). The user
might now change the produced quantity, that's why we round-up when
validating the move: indeed, if the user slightly increase the produced
value (below the uom unit), it actually means he produced more.

This way, instead of not rounding anything and doing rounding behind the
scenes, leading to errors, we round everything and the user sees the
result directly.