Added more properties/types to the angular_ui_router.js externs.

I'm using the UI Router in one of my Angular projects with Closure, and the common externs file could really help out - I'm glad I found this one. Hopefully we can get it all fleshed out soon.

Concerning `ui.router.$state.params` I had a hard time figuring out it's type, so I left it generic.
`ui.router.$state.current` is an instance of `ui.router.State` so this should be `@type` instead of a typedef. Typedef expressions can be used as a new type.