feat(buttons): dynamically add button attributes

Closes #5186

ionic/components/button/test/block/index.ts

@@ -4,4 +4,10 @@ import {App} from 'ionic-angular';
 @App({
   templateUrl: 'main.html'
 })
-class E2EApp {}
+class E2EApp {
+  blockButton = true;
+
+  toggleBlock() {
+    this.blockButton = !this.blockButton;
+  }
+}

ionic/components/button/test/block/main.html

@@ -35,4 +35,8 @@
     <button block round outline>button[block][round][outline]</button>
   </p>
 
+  <p>
+    <button [block]="blockButton" (click)="toggleBlock()">Toggle Block</button>
+  </p>
+
 </ion-content>