Adding flux_visualizations.py for addition of source carbon reaction

[mcnaughtonadm]

File that contains methods required to satisfy temporary addition of source carbon reaction and temporary removal of the bicarbonate to carbon dioxide reaction.

[mcnaughtonadm]

Changed the approach here. Instead of having one "source co2" that gets converted to co2 in the medium and then distributed amongst the individual members, we have 3 separate source exchanges set up. This will take co2_source_m from the medium and exchange it directly into co2_e__Azotobacter, etc. This mimics the behavior of the current medium to extracellular exchanges.

Taking co2 to Azotobacter for example

EX_co2_e__Azotobacter: co2_e__Azotobacter <=> 0.3333333333333333 co2_m
EX_co2_source_e__Azotobacter: co2_source_m --> co2_e__Azotobacter

I left out this 0.3 abundance factor for now to make sure the fluxes visualize correctly. But I will make sure to add this back in before merging.