Add resource icon box for fertility indicators to cityinfo
Island fertility

Yes, this is gathering resource<->building relations in code instead of
our database. Sorry about that. Will look into wiring those in later.

Currently assumes a 0/1 fertility system (either resource A can exist on
island, or it cannot). There are no stepdowns like "half efficiency" for
now and i'm not sure they add that much gameplay value, as opposed to
interface burden and code complexity (which they definitely do add).

As you may have noticed this commit only displays some random icons for
settlements. I'm looking for an implementation of the underlying concept,
even if it's rough and unpolished.
The current mapping for resources against buildings indicates that if an
island is infertile w.r.t. a particular resource, the corresponding
building in MAPPING should be impossible to build in settlements on that
island. Whether to indicate that from our build menus, message widget,
buildability highlights, or a combination thereof, is your call.
Add basic climate zone calculation and adding

Adds a climate zone to each island based on where it is. Islands in the
upper fith of the world will be sub polar, islands in the lower fith
will be desert.
Move climate zone information to yaml files
Assign climate zones to islands and load correct graphics.

At this point atlascreation is still broken.
Fix bugs in climate zone choice, use resources from yaml file
Cleanup and fix a little bug
Add inverse mapping of resource -> building. Use default resources in
fertility on islands
Add sub-polar climate tileset.
Add desert climate tileset.
Disallow building buildings which are in the fertility mapping and for
which required resources are not provided.
Atlases work with the new climate zone tilesets
Temporarily fix editor, mostly to stop gui test complaints
Rename fertility mappings
Line length
Actually mark climate zone names as translatable

They're walked through _() in climate.climatezone.
Not sure why honestly, but here we go.
Fill some more resources into climate zone objects

Not gonna give arbitrary numbers which then go unused, sorry :)
Distribute resources to islands according to their probabilities
Fix a crash in the buildingtool
Add some comments