This change adds the Web API resources defined in an extension's `resources` attribute to the link tree. Now each resource will be added to the 'links' dictionary of the extension resource, and in the list of extensions. These links will only appear when the extension is enabled.

Also fixed is improper generation of the resource URLs. The URLs were generated with the wrong attribute, causing them to use underscores instead of dashes.

Tested with my new extension's resources, and the extensions with resources found here: https://github.com/mikeconley/RB-Toy-Extensions