Farming Update, take 3

Add an attribute "grow" to seeds to allow variable plant growth times.

Tested and it compiles. I'm really hoping to get this merged this time, and I'll do whatever needs to be done to fix it.
Huh? This makes the seed *younger*, it must be older (matured).

The logic in grow_plant was `if(calendar::turn > seed.bday + plantEpoch) { next stage; }`
You changed it to `if(calendar::turn >= seed.bday + plantEpoch) { next stage; }`
That should not require a change here, or am I missing something?