Add AngularyticsProvider.setPageChangeEvent()

Enables the customization of the page change event that is used to automatically generate page view events. This is important for use in ui-router and perhaps other alternatives to default angular routing.

```javascript
AngularyticsProvider.setPageChangeEvent("$stateChangeSuccess");
```
Merge pull request #11 from ggoodman/patch-1

Add AngularyticsProvider.setPageChangeEvent()