Closes #2. Demand previous flows not reset to zero on infeasible solution restart.
Several other fixes are in this commit too:
* Rent pool contributor not limited to capacity minus contribution.
* Storage flow step only links convergence issues due to return flows.
* Reservoirs balanced at every time step rather than as specified in model.
* Reservoir accrual links received less allocation because reservoir outflow
was not included in calculation.
* Owner links to flow thru nodes returns were forced into the storage step, returns
are now available for natural flow allocation.