stockpiles: add settings protobuf message format
install the full protobuf library

required to access text_format (needed by stockpiles plugin)
stockpiles: basic serialization for animals - stone
stockpiles: serialize ammo and coins
stockpiles: serialize through finished goods

* add stubs for remaining categories
* refactor w/ generics to reuse code
stockpiles: serialize through leather

* more code reuse!
stockpiles: serialize through cloth
stockpiles: serialize through weapons+trap components

* generalize itemdefs
stockpiles: serialization complete

* working file import/export
stockpiles: write some documentation
stockpiles: format with ANSI style and  4 spaces
stockpiles: add optional debug output
stockpiles: pass correct filename
stockpiles: import from disk and write to memory
stockpiles: fix male/female creature mat lookups
stockpiles: add missing protobuf field
stockpiles: allow loading without file extension
stockpiles: fix quality unserialization
stockpiles: handle furniture sand_bags field
stockpiles: fix finished goods quality