Fix rtl issue take 2

@pfiller This builds upon the idea in this PR https://github.com/harvesthq/chosen/pull/1096#issuecomment-16824258 except it's toggling a css class to do the positioning.

* LTR select boxes will position `left: -9000px`
* RTL select boxes will position `left: 9000px`
* The scrollbar issue will still exist if you have both RTL and LTR on the page (fixed for demo page)
* The scrollbar issue will still exist if the page isn't set in the same direction as you've set the select box (fixed for demo page)

cc: @stof, @ido-ran, @krembo99