PotionDateTimePicker

[bmichotte]

This PR adds DatePicker and TimePicker

# show datepicker
PotionDateTimePicker.new do |time|
  mp time.to_s
end

# show timepicker
PotionDateTimePicker.new(type: :time) do |hour, minute|
  mp "#{hour}:#{minute}"
end

There are few options like :time, :hour, ...

[jamonholmgren]

I'd recommend using a class method show (instead of new instantiator) to make it obvious that you're showing the picker.

# show datepicker
PotionDateTimePicker.show do |time|
  mp time.to_s
end

[bmichotte]

I added this method