refactor(bootstrap): Remove support for old bootstrap mechnanisms

Remove support for bootstrap detection using:

* The element id
* The element class.

E.g.

```
<div id="ng-app">...</div>
<div class="ng-app: module">...</div>
```

Removes reference to how to bootstrap using IE7

BREAKING CHANGE:

If using any of the mechanisms specified above, then migrate by
specifying the attribute `ng-app` to the root element. E.g.

```
<div ng-app="module">...</div>
```

Closes #8147