crop field clustering, extends, multi-assign & big structures

1. Auto-cluster fields. so if you build like a 10x5 area, you will get like 3 sub-fields out of it. they could be separated by small pathes between and ladders if there's elevation. it should feel like one big thing, but you should be able to assign multiple workers to it. it should be configurable somehow

2. be able to extend - for upscaling, especially later in game, it should be possible to not require the user to build a new field, but rather extend the existing one with more plots. that should then redo the clusters but keep the assigned villagers and crops. upscaling basically. removing could also be possible but options.

3. add new structures that already have multiple fields, famous example are the rice terraces (tanada), could even be a special project somewhere to better blend with the environment.