Added support for iOS7 appearance.

Allows for setting barTintColor and tintColor to change the look of the Reader.
Example:

	ReaderViewController *readerViewController = [[ReaderViewController alloc] initWithReaderDocument:document];
	[readerViewController setBarTintColor:[UIColor colorWithRed:0.1 green:0.3 blue:0.8 alpha:0.9]];
	readerViewController.view.tintColor = [UIColor colorWithWhite:1 alpha:1];

This sets both the toolbar and pagebar background color. The buttons and the Done-button text automatically changes color to the tintColor of the ReaderViewController.

iOS 6 still uses the old appearance.