[ALOY-1259] Alloy: The code in alloy.js should be wrapped by app.js to protect global scope

The code a developer adds to app/alloy.js will simply be injected into the generated Resources/<os>/app.js file as can be seen in the [template](https://github.com/appcelerator/alloy/blob/master/Alloy/template/app.js). Unlike the CommonJS modules that make up the rest of an Alloy app, all variables in this file will be part of the global scope. We could enforce a best practice to not pollute the global scope by wrapping the imported code in a self-executing function like this:

(function(exports) {
	
__MAPMARKER_ALLOY_JS__
	
})(this);

This way, the developer can still force to set a global by using exports.foo = "bar"; just like they export variables in controllers.

Warning

This **will** break apps that depend on globals set in alloy.js, other then those using Alloy.Globals.