refactor(spec/basic): create and make use of a new bindings PageObject

* Created a PageObject for the bindings page, which is a page in the testapp
* Updated `spec/basic/findelements_spec.js` to use the new PageObject
* Protractor recommends using [PageObjects](https://github.com/angular/protractor/blob/master/docs/getting-started.md#organizing-real-tests-page-objects) for writing tests. This is an initial attempt to use the pattern in the Protractor test code.