[ALOY-1704] Allow Alloy Widgets to be discovered by package.json properties

Currently, you can install a Titanium Alloy widget via npm but it is required that the naming of the widget match the pattern "alloy-widget-*". It also requires that the widget be added to config.json in the app. This method is not very flexible as it doesn't support any scoped npm packages. What would be much better is to include a property in the package.json file (similar to what native Titanium modules on npm do) and bypass the requirement that the widget be added to config.json. Basically the dependency in package.json would replace config.json and the titanium json property in the package.json would replace the existing naming convention.