buttonMarkup called many times on init

I found that buttonMarkup is called many times on the same objects at init.
- Slider - calls with the same params in create and refresh (which is called by create...)
- Button - in refresh calls again only to send option disabled true/false - disabled param is ignored by buttonMarkup but I didn't remove it.
- Checkboxradio - calls again to determine checked state and change icon

I made 3 commits because Slider is a bug and should be merged, in 2 others I use solution which may not be accepted :)

buttonMarkup is also called again on the same objects when controlgroup and rangeslider is used - both widgets call refresh on checkboxes and sliders inside them. I haven't found solution yet. This should probably fixed in other way.