angular-resource.d.ts. parameter of IResource<T> change to optional

@miffels @scottmcarthur I want to change parameter of IResource<T> change to optional.
Can I merge this PR?

this PR is not beautiful. but I think this hack is useful.
https://github.com/Microsoft/TypeScript/issues/371
If this proposal are accept by MS, this PR is unnecessary :)
Add:
```
// Important!: All members are marked optional to make it easier for you to extend this in your classes without having to list all the members (See TypeScript issue : https://github.com/Microsoft/TypeScript/issues/371)