add new appointments by clicking on day

Add the capability to add a new appointment to the calendar by clicking on the day the appointment should be scheduled for. Clicking on a particular day in the calendar opens the 'Create Appointment' dialog and pre-populates the values of 'Starts on' and 'Ends on' with the day it was clicked on.

This works in Google calendar. In my opinion

• this is very intuitive,
• it saves on the effort of entering the details of an appointment by pre-populating the values of the fields 'Starts on' and 'Ends on', and
• it aligns with a UI that users coming from Google Calendar might be used to.

As of now there isn't any functionality assigned to clicking on a day in the calendar, so this does not interfere with any existing UI.