pep8 loadflow.py
Hard coded some unscheduleable generation.

To start adding wind we need to be able to have some generators that cannot change their output. Their output is only changed in fix_mismatch so if we never give fix_mismatch the unscheduleable generators their values wont change. This has quickly been tested with `main.py test` and keeps the same total power after and also keeps the fixed generators power fixed.

There was no particular reason why G23, G56 and G89 were chosen. They are the biggest and hence should make the biggest impact.