feat(checkbox): stand-alone checkbox components

ionic/components/checkbox/test/basic/index.ts

@@ -26,6 +26,7 @@ class E2EApp {
 
     this.grapeDisabled = true;
     this.grapeChecked = true;
+    this.standAloneChecked = true;
   }
 
   toggleGrapeChecked() {

ionic/components/checkbox/test/basic/main.html

@@ -48,6 +48,11 @@
     <button (click)="doSubmit($event)" outline small class="e2eSubmit">Submit</button>
   </p>
 
+  <p>
+    <ion-checkbox [(ngModel)]="standAloneChecked"></ion-checkbox>
+    Stand-alone checkbox: {{standAloneChecked}}
+  </p>
+
   <p aria-hidden="true" padding>
     <code>appleCtrl.dirty: {{fruitsForm.controls.appleCtrl.dirty}}</code><br>
     <code>appleCtrl.value: {{fruitsForm.controls.appleCtrl.value}}</code><br>