Ability to specify tab info by array

Add arrays containing tab titles and images to AKTabBarController,
allowing for these properties to be specified without changing each
individual view controller.

Adds properties:

    @property (nonatomic, strong) NSArray *tabTitles;
    @property (nonatomic, strong) NSArray *tabImageNames;
    @property (nonatomic, strong) NSArray *tabActiveImageNames;
    @property (nonatomic, strong) NSArray *tabBackgroundImageNames;

These arrays must match the length of the viewControllers array.

To specify only specific values via array, use [NSNull null] as
a placeholder.  From AKTabBarExample AppDelegate.m:

    _tabBarController.tabTitles = @[
	    [NSNull null],
	    [NSNull null],
	    [NSNull null],
	    @"Link!",
	    ];

This will override the fourth tab's title.
Add array setters & trigger tab reload
Example usage of arrays to override titles & images
Merge branch 'specify-tab-names-and-images'