Add TimepickerField to CalendarDateTime time fields

[sheadawson]

... If the user has the module is installed. Perhaps put that as a suggestion in the composer.json also.

https://packagist.org/packages/silverstripe/timepickerfield

I'm potentially going to be making some heavy use of this module in the coming months, just making some notes of pull requests I'll be submitting soon ;)

[unclecheese]

I have no problem adding time picker field as a dependency if you want to make a PR that makes the module rely on it.