WIP: Platform Specific Config

We want to move ahead with more aggressive platform-specific styles for iOS, Android, and soon Windows Phone and BB 10.

What this means is that by default the style on Android will have left aligned titles, not use the sliding animation for navigation, not bounce in scroll (already done), and have tabs on top (as an example).

To that end, we need to come up with a nice API for handling platform specific changes and being able to configure them. `$ionicPlatform` is already a provider which makes it easy to inject into the `config()` function. What should the API look like for this?

Here is my proposal:

```javascript
angular.module('myApp', ['ionic'])

.config(function($ionicPlatformProvider) {
  $ionicPlatformProvider.set('navTransition', 'my-custom-slide-transition');
  
  // With object syntax:
  $ionicPlatformProvider.set({
    navTransition: 'my-custom-slide-transition',
    titleTransition: 'my-custom-title-transition',
    tabsPosition: 'top'
  });
});
```

This allows you to override the platform defaults if you like.

Can we come up with a better API?