move constructions to json

also ended up removing the idea of "stages",
or rather the stages are just determined by what you have done so far.

so now, you can dig a pit, and then continue to turn it into a log wall, or a palisade wall, or put spikes in it if you want to do that in stead.

in addition, i ended up making it so that only things you could theoretically build (if you had the tools) are shown. That way the construction display isn't cluttered with things you aren't going to build, and many more constructions should be able to be added (especially ones that depend on other constructions being built first) without overwhelming the player.

all this because i wanted to be able to turn an empty window frame into a wall.

actually i completely forgot to add that…