Cotton plants used to drop strings, now they drop farming:cotton. Some mods (namely, throwing) still use farming:string, therefore we need farming:string to be equal farming:cotton.

- API {farming.register_hoe(), farming.register_plant()}
- Fertilities -> Plant only grow on soil with a fitting fertility, e.g. Wheat only grows on grassland, while cotton grows in deserts and grassland)
- New soil: Desert Sand
- Place seeds instead of plants

Also, move "waving = 1" property for grasses/shrubs over to default/nodes.lua
and put all instances of this property right under the drawtype, since they
are directly related and depend on the above.