Code review comment for lp:~charlesk/indicator-datetime/cpp

I've built/tested that a bit on my trusty desktop, it seems to work mostly fine (even fixing some bugs on the way like the tz change not being picked up or the week number setting not applying until restart), good work!

Small user comments:
- the "add an event" item is not enabled while I've evolution installed (that used to work)
- toggle the preference to show or not the calendar widget doesn't work dynamically