Better scale dependency

I have changed the scale dependency levels for automatic zooming and maximum zoom levels.

Basically you get to the higher resolution data quicker, I think this will be acceptable once the new caching code has gone live.

This pull will reduce maps like this:
![image](https://cloud.githubusercontent.com/assets/1215415/2927259/24ac9140-d769-11e3-8d5c-9a7edf14bee5.png)

and make them:

![image](https://cloud.githubusercontent.com/assets/1215415/2927261/367b3fde-d769-11e3-8e4a-16f39be0a07b.png)