Active visit portlet on dashboard should show date + time in a prettier way

On the "Active Visit" portlet towards the top of the page, if the start date is today or yesterday, then instead of showing the date as "dd/mm/yyyy", it should instead say "Today hh:mm" or "Yesterday hh:mm". Older dates should be "dd/mm/yyyy hh:mm". (Obviously, use the current date/time format for dmy vs mdy, and for am/pm vs 24-hour time.)

Add this as a feature to the openmrs:formatDate tag.