Get rid of the Geometry class

Legacy from the time I was using the PythonMagick bindings.
Introduce the concept of Regions

It turns out we have way too many raster images, specially on big
cities. A lot of these images are hidden and are never rendered. This
patch is the early bits of a trivial scene graph implementation.

The major goal will be to render cities by regions of clamped images and
do not add to the .vrt images that are completely occluded.
Add occlusion culling

A trivial hit test to discard images that are not exactly visible.
On the next step I will add image grouping so we won't do the hit test
on the empty areas of the map.

Testing with Para de Minas, half of the images were discarded and I did
not notice any difference on the final result. \o/
Group images by Regions

This is outstanding optimization. Usually a city has a lot of other
districts in remote areas. If we consider everything as a single map, we do
a lot of computation in the areas within these districts, and they are
just empty spaces.

In the future patches adding support for .mbtiles, we are going to do
exports by Regions. A single city like Para de Minas, will generate 8
.mbtiles and thus, 8 data exports. The performance gain is massive,
since they can be done in parallel and we do not generate transparent
tiles for the areas in between.