Options to display navigation title icon and cell title icon.

[beata]

Hi, I've done some work for displaying icon on navigation bar and table cell.

1. Prepend icon to navigation title.
2. Prepend icon to table cell title.
3. Add new init() parameter itemImages:[UIImage]? = nil
   If set, the corresponding item image would be added to each table cell.
4. Add new configuration option shouldChangeTitleImage
   If set to true, the icon of the selected item would be presented on navigation bar.
5. Add new configuration option iconImage
   A placeholder used for cell item postioning.
6. Update touch area in layoutSubview to avoid small touch area problem.