AutoResizeContainer for city info

Makes more sense when you're changing the content frequently
(which i will, testing out some things).
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
Desert zone tile placeholders

Old moderate tileset + convert -fill yellow -tint 137,88,0,30
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.