Added generics to IHttpPromise and some missing properties/overloads

I know you haven't used generics so far so I hope this is a welcome
change - the only nuisance is that it will "break" current compilation
but will increase type safety by far.

Also added params to ICurrentRoute and inline injection notation to
$provide.decorator as per
https://github.com/borisyankov/DefinitelyTyped/issues/799