Fixed bug about left moving
Added action and target
Fixed: CPDatePicker works with action and target

Previously the CPDatePicker didn't work with the action and target. Now each time the dateValue changed, the given action is sent to the target.
This commit fix also a bug with moving with tab and the arrows. Before, the left arrow worked liked a tab when the firstElementTextField was selected in a textual CPDatePicker.

Test app in Tests/Manual/CPDatePicker.
Merge branch 'CPDatePickerTarget' of https://github.com/Dogild/cappuccino into pr-1895