New Features and Options

Hi,

This commit have:

* Support for esri-leaflet DynamicMapLayer
* Support for ESRI Legend Service.
* Support for custom layers control.
* New options for layer controller: 

```
controlLayersPosition  //removed

// New options
controlLayers: {
	position:'topright',
	control: L.control.layers,
	collapsed: true
}
```

With these new options, the control layer can be any plugin that extends L.Control.Layer.

Hope you like it :+1: