Fix rtl issue take 2

@pfiller This builds upon [the toggle classname PR](https://github.com/harvesthq/chosen/pull/1157), which I'm about to close. The changes are small enough that it can be reviewed in this one.

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.

cc: @stof, @ido-ran, @krembo99