Allow remote method name to be customized using alias

/to @ritch @bajtos 

The PR is the first step to fix the issue that our internal method names such as `__get__subscriptions` to be exposed to REST APIs and AngularJS resources. With the enhancement, we can now customize the remote method name as follows:

```js
MyModel.__my_method = function() {};
MyModel.__my_method.alias = 'myMethod'; // or MyModel.__my_method.operationName = 'myMethod'; 
MyModel.__my_method.shared = true;
```