Plant food boost.

- Plant food recipe gives 4 times the amount of plant food now.
- Recipe requires 4 times the amount of water. (Reduces time spent on creating it, and reduces amount of chemicals used for the recipe).
- Increased time reduction by plant food by 50% (was 2 days, is 3 now).
- Changed the time reduction to give a 20% reduction depending on season length. On default this gives 2.8 days reduction.

As discussed in:
http://smf.cataclysmdda.com/index.php?topic=5823.0