Plowing with a cultivator

Adds an "Operating mode" configuration to compatible cultivators with two options: "Cultivation" and "Plowing".

In "Plowing" mode, the implement works like a regular cultivator and leaves cultivated soil behind, but the field is also considered plowed and no longer requires plowing.
In "Plowing" mode, the standard "Allow create fields" function is available, so the cultivator can be used to create new fields.