Now support customized toolbar item text attributes.

This fix allows for the customization of the footer's `UIBarButtonItem` global-appearance text attributes without `CTAssetPickerController` overriding it.

For example:
```objective-c
[[UIBarButtonItem appearance] setTitleTextAttributes:@{NSFontAttributeName:[UIFont systemFontOfSize:10], NSForegroundColorAttributeName: [UIColor whiteColor]} forState:UIControlStateNormal];
```

Another alternative to this fix could be to remove from `CTAssetsPickerController.m` the code that sets the footer's `UIBarButtonItem` text attributes.