Simplestyle

NOTE: Merge #2148  and #2161 before even looking at this (since the diff is overly large without them).

I would like to get this into 1.2, if possible.

* Added `GeoJson.fromUrl` to make it easy to add a data source in less code.
* Added support for the GeoJSON [simplestyle specification](https://github.com/mapbox/simplestyle-spec). [Sandcastle example](http://localhost:8080/Apps/Sandcastle/index.html?src=GeoJSON%20simplestyle.html);
* Added `PinBuilder` class for easy creation of map pins. [Sandcastle example](http://localhost:8080/Apps/Sandcastle/index.html?src=PinBuilder.html);
* Added `Color.brighten` and `Color.darken` to make it easy to brighten or darker a color instance.
* Changed default `GeoJSON` Point feature graphics to use `BillboardGraphics` with a blue map pin instead of color `PointGraphics`.

Here's what the pins generated by the new `PinBuilder` class look like:
![image](https://cloud.githubusercontent.com/assets/1495196/4452134/fb3e54b6-4841-11e4-8d7b-3554d6e98dda.png)

There are 3 things going on.
1. The simplestyle spec says `title` should be used for the name, so the first thing we do is check for `title` directly.
2. If that fails, we loop through all keys looking for a case insensitve match of the word `name` or `title` (hence the toLowerCase instead of regex, we don't want a partial match).
3. If that fails, we loop through again looking for any property that's a partial match to `name` or `title`.

This might be overkill, so I'm okay with simplifying it (probably by using an exact match only and deleting the partial match loop).  But there's no harm in keeping it either.  That being said, I found an issue with the code and I'm going to do a quick cleanup of it.