Throttle surveys shown per day

- Add a check to showSurveyNotification to only proceed if we're under some maximum number of surveys to show each day.
- Add an alarm to reset the count of surveys shown to 0 each day.

This fixes issue #31 
nit: I prefer to leave off the { } if it's a one-line if-statement. Everyone has different feelings about this but it makes the code a little shorter.