Add a legend to the web map example

[tomwayson]

Also use the load event instead of esriRegistry to get a handle to the map object.

Updating the example w/ these changes will help me verify a couple of things that I'm not sure are currently working w/ the web map:

• will load event even fire if using a web map?
• should we be setting the esriMap directive's layerInfos using arcgisUtils.getLegendLayers(response) (as shown in this sample) after loading from a web map (regardless if the page includes a legend)?

I think the best case scenario right now would be that it shows all layers in the legend. Worst case would be that the legend doesn't even work.

[tomwayson]

After a quick test, I can say for sure that the map load event is not firing when using a web map.

I've opened a bug for this, see #75

[tomwayson]

Yep, we did indeed need to be setting the esriMap directive's layerInfos after loading the web map. Without that, it was showing all layers (including the basemap and the basemap labels, etc). After adding it, it showed only the layers as defined in the web map.

This is fixed in 1d64834