Dagger unused member injection check

When doing members injection with Dagger, IDEs can no longer detect fields as unused due to the members injector referencing every field. Having error-prone fill this gap can ensure the minimal subset of bindings are always used when doing members injection.

Example:
```java
class FooActivity extends Activity {
@Inject BarManager barManager;
@Inject BazManager bazManager;

@Override public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
AndroidInjector.inject(this);

TextView tv = new TextView(this);
tv.setText(bazManager.getBaz());
setContentView(tv);
}
}
```