refactor(checkbox): added tons of vars and modified some, flattened markup, renamed elements

changed color of checkmark so lighters backgrounds would be visible &
added the light example, references #689

ionic/components/checkbox/test/basic/e2e.ts

@@ -1,6 +1,6 @@
 
 it('should check apple, enable/check grape, submit form', function() {
-  element(by.css('[ng-control=appleCtrl] media-checkbox')).click();
+  element(by.css('[ng-control=appleCtrl] .checkbox-media')).click();
   element(by.css('.e2eGrapeDisabled')).click();
   element(by.css('.e2eGrapeChecked')).click();
   element(by.css('.e2eSubmit')).click();

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

@@ -28,6 +28,10 @@
         secondary color
       </ion-checkbox>
 
+      <ion-checkbox light checked="true">
+        light color
+      </ion-checkbox>
+
     </ion-list>
 
   </form>