iOS 7 style back button for iOS 5 + 6, fixes for text clipping on flat back button (iOS 5 + 6), and importing UIToolbar in FlatKit.h

#### minor change 

imports `UIToolbar` category into `FlatKit.h` (https://github.com/Grouper/FlatUIKit/pull/81)

#### fixes  

 * problem with back button not tiling correctly if the title of the button is too long.

![2013-08-06_12-37-45](https://f.cloud.github.com/assets/466104/916402/ebab85f6-fe8b-11e2-8a3a-6b936f998f0d.png)

#### improvement:  

1. adds` UIBarButtonItem` category method:   `setTitleColor: highlighted: removeShadow:` to help configure bar button items
2. adds a second category on `UIBarButtonItem` to provide an iOS 7 style back button for iOS 5 + 6.

![2013-08-06_12-53-07](https://f.cloud.github.com/assets/466104/916404/08e034aa-fe8c-11e2-8141-f0b12b9606fe.png)