splays a shutter control
*
* @param {id=} unique id for this widget (optional)
* @param {item(num)} an item for the position of the blinds
* @param {item(num)=} an item for the angle of the blinds (optional)
* @param {value=0} the value for opened (optional, default 0)
* @param {value=255} the value for closed (optional, default 255)
* @param {value=5} step between two values (optional, default 5)
* @param {text(half,full)=half} 'half' blade turns from -1 to +1, 'full' blade turns from 0 to +1 (optional, de