Changes to plant food

-plant food renamed to liquid fertilizer
-plant food is now entirely beneficial to those with MUTCAT_PLANT as their highest category
-plant food will give higher bonuses with higher levels of mutation

//This effect can alternatively be accomplished by cluttering up player.cpp's consume and consume_effects,though it may not be worth it for only a single consumable. With this branch's method negative effects are applied and then immediately reversed using this method.
//Seems fair enough to use highest, though a player with high levels of plant and higher level of another mutation category will still get harmful effects.

May need updating if #6564 ever gets implemented.