[#13] Begin refactor extracting choroplethmap creation from CKAN's module

The final aim is having a reusable choropleth map which knows nothing about
CKAN's resources. We might not achieve that, but at least I want to be able to
have a choroplethmap CKAN module, and a regular map (or navigationalmap)
module, one which creates a choropleth, and other that creates a regular map,
reusing as much code as possible.
[#13] Extract NavigableMap from ChoroplethMap

The basic difference is that ChoroplethMap has a resourceValueField, which will
be used to plot the different colors, while NavigableMap doesn't.
[#13] ChoroplethMap's JS reuses NavigableMap's

There's still too much code duplication, but we're starting to get there.
[#13] Extract map's ckan module creation to a separate file

First of all, the visualizations shouldn't know about CKAN. I also removed
quite a bit of code duplication doing this. I had to add some magic to do this
(by using the same initializer, just changing the type of map to be called),
but I think it's better than it was before.
[#13] A navigable map doesn't need the resourceValueField

Every region has the same color, independent on its value.
[#13] Change navigable's map color to a nice blue
[#13] Pass only the geojson object to the maps

What jQuery gives us back is the object, success state, and a few callbacks.
They just need the object.
[#15] Ignore rows with no region in the geojson when creating the choroplethmap

This helps us find the best scale for the data that's going to be plotted,
without allowing an outlier in the data which isn't going to be drawn anyway
to screw things up.