Resource building creation

[CptCrispyCrunchy]

In the current state of the module, buildings get only placed in the city boundaries. However it would make sense to introduce buildings outside of the main city area, like farms, mines, etc. There is already a foundation to build upon: Region tiles, which can save (and already do save to a certain extend)
information about the resources and terrain. Hence this one should be relatively straight forward as it just puts together a lot of existing mechanics.
First the region tiles in the outskirts of the city have to be sorted for the relevant resource.
A DynParcel with the corresponding resource building can then be placed on the tile with the highest amount of resource.
The amount of resource buildings should orientate itself on the cultural needs and maybe even on the market dynamics.
Reasonable threshold values should be found for the amount of resources of a tile to qualify for building placement.

[jdrueckert]

@skaldarnar IIRC that's what districts are for, right? Or am I mixing something up here.
If not, then we can probably close this?