Replace custom htmlPopupExtensions with built-in equivalents

[JeffJacobson]

The functionality of htmlPopupExtensions.js is now possible with built-in methods in the JavaScript API. Eliminate htmlPopupExtensions.js and modify the code for handling configurations to use the built in methods.

This should fix issue #20.

• [ ] Remove htmlPopupExtensions.js module.
• [ ] Turn on enableInfoWindowOnClick in esri/Map constructor
• [ ] Modify configuration to use ArcGIS REST API Web Map format for popup definitions (instead of server-defined HTML popups).