Slider: remove duplicated call to buttonMarkup
Button: remove duplicated call to buttonMarkup
Checkboxradio: remove duplicated call to buttonMarkup
Checkboxradio: Extend widget instance with buttonMarkup options and empty object after use.
Revert "Button: remove duplicated call to buttonMarkup"

This reverts most of ommit 546fc7237e3502f42c3d56476dacbfb13e2f0b24.
Functional tests: Button markup: Remove reference to jqm-docs.css.
Button: Implement widget(), _destroy(), and perform _setOptions() via buttonMarkup()