Prevent bubbling of click events

[Wartybliggens]

A big problem I have run into with react-kronos is that click events escape, since kronos does not use event.preventDefault() for clicks on the date chooser dropdown.

Imagine this scenario:

• A modal overlay with a form in it, including react-kronos.
• The modal is set up so that clicks outside the modal auto-close it.
• When the user clicks on the react-kronos dropdown (since it's an absolutely-positioned div, not a child of the modal), it counts as an outside click, so the modal closes. Sorry!

I imagine it would be a pretty simple changeset to address this. At some point I may try and do a pull request if you don't get to it.