Xubuntu UIFe: Replace the current clock in the panel with xfce4-datetime-plugin

I'm proposing a UIFe for replacing the clock in Xubuntu's default top-panel with the xfce4-datetime-plugin. This plugin provides extra functionality as it pops up a calendar when clicked upon and I think this would be very useful (and most likely expected behavior) for our users.

The datetime-plugin can be formatted just like the clock-plugin, so visually nothing would change.