handle checkbox ask like list.ask, by adding options in a hash

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
added checkbox specs (simple)

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
bugfix: don't do anything if checkbox has no items

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
add specs for moving and selecting around the checklist

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>