Reduction problem size by adding conditions on constraint construction

[willu47]

I've added a few small conditions to constraints following these rough guidelines:

• trade constraints should not be created when r and rr are equal
• all constraints with Produce only need to be generated when there are corresponding non-zero values in the OutputActivityRatio
• all constraints with Use only need to be generated when there are corresponding non-zero values in the InputActivityRatio
• Also fixed an issue with incorrect index in constraint OC1 causing the variable cost to be calculated for every timeslice.