added hide_mode option

With hide_mode option the hide method for the dropdown can be changed to prevent different problems. 

"hide_mode: null": uses "'left': -9000" (its still the default to not break compatibility), can be problematic with very wide pages or with RTL.

"hide_mode: display": uses display hide/block, should be the most performant solution, but can result in uncorrect position/dimension calculations

"hide_mode: visibility": should be the most compatible version