TIMOB-6053 - Android: fontStyle support added

Fixed bug TIMOB-6053 - Android: fontStyle not supported on Android 

Modified TiUIHelper.styleText to read fontStyle and use it in TiUIHelper.styleText.
An overloaded styleText is added to handle the additional fontStyle parameter. 
Existing styleText is modifed to call the new method so that existing code that doesn't pass styleText doesn't break.