rxjava-android: parameterize OperatorViewClick by concrete view type

[Yarikx]

Parameterize OperatorViewClick observable to actual View type.
So actual view with it native type can be used.

So instead of

Observable<View> imageClicks = ViewObservable.clicks(imageView, false);
        //...
        imageClicks.subscribe(new Action1<View>() {
            @Override
            public void call(View view) {
                ImageView imageView = (ImageView) view;
                imageView.setImageBitmap(bitmap);
            }
        });

you can use

        Observable<ImageView> imageClicks = ViewObservable.clicks(imageView, false);
        //...
        imageClicks.subscribe(new Action1<ImageView>() {
            @Override
            public void call(ImageView view) {
                view.setImageBitmap(bitmap);
            }
        });

[benjchristensen]

/cc @mttkay for review as it is for Android.

[mttkay]

Looks good to me.