Hack to set compi for producer.
compi is set to [0 1 0] for all producers
Merge remote-tracking branch 'totto82/add_compi_producers' into add_compi_producers
Use preferred phase of producer well to set comp_fraction.

This replaces the previous hack, that set comp_fraction to (0,1,0) always.
Changed documentation of Wells::comp_frac to match reality.
Merge pull request #564 from atgeirr/add_compi_producers

Add Wells::comp_frac for producers