Button: Fixed the bugs of _setOptions - The button widget doesn't set the icon option.

Hi All~! :)

My team found bugs on _setOptions, and first, fixed a bug that the button widget doesn't set the icon option. 
So I'll submit PR.

You can see on the following test pages.
* origin: http://hyunsook.github.io/jqm-debug/latest/buttons-button_setoptions_icon_origin.html
* modified: http://hyunsook.github.io/jqm-debug/latest/buttons-button_setoptions_icon_after.html

Additionally, my team will fix bugs of the other options of button widget and I'll submit PRs immediately when it is completed.