Update foundation.dropdown.js to allow user defined "right aligned" dropdown (redux)

Changed functionality to be 'options' based, as per suggestion by @mhayes on previous PR: https://github.com/zurb/foundation/pull/2905#issuecomment-24429915
Merge pull request #3260 from nhodges/patch-2

Update foundation.dropdown.js to allow user defined "right aligned" dropdown (redux)