Allow Label to wrap at hyphens

This commit will allow the Label to break at the hyphen (-) character, as well as whitespace.
This is optional; default behavior remains the same.
This was suggested in #2486 
Behaviour has been tested:
![labelwraptest](https://cloud.githubusercontent.com/assets/7389241/4760029/415553e8-5aec-11e4-9b96-4aaf7b7f3130.PNG)


`BitmapFont#getWrappedBounds` needs this same change. Also, I guess `BitmapFont.isWhitespace` can be deleted and `isBreakChar` can return true for whitespace.