Docs for beta 6

Adds the following docs for beta 6...

* `createfeature`, `addfeature` and `removefeature` events.
* `query()` on `MapService` and `ImageService`
* New methods on `L.esri.Tasks.Query` for supporting `MapService` and `ImageService`

@robertd I also have commented out the link to `L.esri.RasterLayer` in the sidebar. I did this because I don't want base classes like `L.esri.RasterLayer` and `L.esri.FeatureManager` quite yet. These are pretty key parts of the ecosystem but I want to document them as "Base Classes" and give detailed examples of how to extend them to create your own visualization. Users might be confused about using `RasterLayer` vs `ImageMapLayer` vs `DynamicMapLayer` and I want to make sure we dont run into that.