[Android] Fixed i18n of Cancel label and fixed cancel callback

Fixed issue https://github.com/VitaliiBlagodir/cordova-plugin-datepicker/issues/4 and https://github.com/VitaliiBlagodir/cordova-plugin-datepicker/issues/28

The cancel button labels are internationalized and are using android.R.string.cancel instead of the hardcoded "Cancel" label.

When the user pressed cancel, the callback in android was not fired because it checks for isNaN and does nothing if the parameter is not a number.