Fix bboxes

Some bboxes are in (left, right, lower, upper) and some (left, lower, right, upper). This should be unified.

namedtuple could be a good way to handle bboxes.

```
from collections import namedtuple
BBox = namedtuple("BBox", "xmin ymin xmax ymax")
bbox = BBox(24, 60, 25, 61)
print(bbox.xmin)
```