refactor(refresher): allow refresher content customization

Breaking Change:

## Refresher:

- `<ion-refresher>` now takes a child `<ion-refresher-content>`
component.
- Custom refresh content components can now be replaced for Ionic's
default refresher content.
- Properties `pullingIcon`, `pullingText` and `refreshingText` have
been moved to the `<ion-refresher-content>` component.
- `spinner` property has been renamed to `refreshingSpinner` and now
goes on the `<ion-refresher-content>` component.
- `refreshingIcon` property is no longer an input, but instead
`refreshingSpinner` should be used.

Was:

```
<ion-refresher (refresh)="doRefresh($event)"
pullingIcon="arrow-dropdown">
</ion-refresher>
```

Now:

```
<ion-refresher (refresh)="doRefresh($event)">
  <ion-refresher-content
pullingIcon="arrow-dropdown"></ion-refresher-content>
</ion-refresher>
```

ionic/components/scroll/test/pull-to-refresh/index.ts

@@ -1,39 +0,0 @@
-import {App} from 'ionic-angular';
-
-
-@App({
-  templateUrl: 'main.html'
-})
-class E2EApp {
-  items = [];
-
-  constructor() {
-    for(let i = 0; i < 20; i++) {
-      this.items.push({ "index": i });
-    }
-  }
-
-  doRefresh(refresher) {
-    console.log('Doing Refresh', refresher)
-
-    // Add to the top of the list on refresh
-    let firstIndex = this.items[0].index - 1;
-
-    for(let i = firstIndex; i > firstIndex - 5; i--) {
-      this.items.unshift({ "index": i });
-    }
-
-    setTimeout(() => {
-      refresher.complete();
-      console.log("Complete");
-    }, 5000);
-  }
-
-  doStart(refresher) {
-    console.log('Doing Start', refresher);
-  }
-
-  doPulling(refresher) {
-    console.log('Pulling', refresher);
-  }
-}

ionic/components/scroll/test/pull-to-refresh/main.html

@@ -1,18 +0,0 @@
-<ion-toolbar><ion-title>Pull To Refresh</ion-title></ion-toolbar>
-
-<ion-content>
-  <ion-refresher
-    (start)="doStart($event)"
-    (refresh)="doRefresh($event)"
-    (pulling)="doPulling($event)"
-    pullingIcon="heart"
-    pullingText="release to refresh..."
-    refreshingIcon="star"
-    refreshingText="refreshing...">
-  </ion-refresher>
-  <ion-list>
-    <ion-item *ngFor="#item of items">
-      Item {{ item.index }}
-    </ion-item>
-  </ion-list>
-</ion-content>