refactor(overlays): inject overlay providers

BREAKING CHANGES:

- Overlay components, such as Alert or Modals, should now be created
using its injected provider.
- Overlays now have the `present()` method on the overlay’s instance,
rather than using `nav.present(overlayInstance)`.
- All overlays now present on top of all app content, to include menus.
- Below is an example of the change to `Alert`, but the pattern is the
same for all overlays: ActionSheet, Loading, Modal, Picker, Popover,
Toast

WAS:

```
import { NavController, Alert } from ‘ionic-angular’;

constructor(private nav: NavController) {
}

doAlert() {
  let alert = Alert.create({
    title: 'Alert',
  });
  this.nav.present(alert);
}
```

NOW:

```
import { AlertController } from ‘ionic-angular’;

constructor(private alertCtrl: AlertController) {
}

doAlert() {
  let alert = this.alertCtrl.create({
    title: 'Alert'
  });
  alert.present();
}
```

src/components/nav/nav-options.ts

@@ -0,0 +1,14 @@
+
+export interface NavOptions {
+  animate?: boolean;
+  animation?: string;
+  direction?: string;
+  duration?: number;
+  easing?: string;
+  keyboardClose?: boolean;
+  preload?: boolean;
+  transitionDelay?: number;
+  progressAnimation?: boolean;
+  climbNav?: boolean;
+  ev?: any;
+}