Update chosen-rails

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Added ability to clear milestone/assignee during bulk update

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
Minor ui fixes for selects at issues page

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>