Updates the MR cost quantity and linecost based on the percentage entered.
If the MR line quantity is null, then the percentage applies to the linecost,
otherwise it applies to the quantity. While calculating these values, MR cost
lines totals are kept equal to the MR line values.
Conditions :
- If the sum of the percentages is 100,
set the quantity on the MR cost line as the difference between the
quantity on the MR line and the sum of quantities on the other MR cost lines;
set the linecost as the difference between the linecost on the MR line and the sum of the MR cost linecosts of the other MRcost lines
- If the sum of the percentages is not 100,
set the MR cost quantity = quantity * percentage/100;
set the MRcost linecost=linecost * percentage/100