Add analytics to the models

[Levi-Lesches]

Insert calls to Services.instance.analytics in the following places:

• setUserGrade in UserModel.init
• onCreateReminder in Reminders.addReminder and Reminders.replaceReminder
• onDeleteReminder in Reminders.deleteReminder, to understand how repeat/one-off reminders are used
• onUseScheduleDropdown in ScheduleViewModel.update
• onUseScheduleCalendar in ScheduleViewModel.date= (it's set date(DateTime date))
• adminOnCreateSchedule in AdminScheduleModel.createSchedule and .replaceSchedule
• adminOnEditCalendar in CalendarEditor.updateDay

This is a nice issue to tackle because it shows intuitively where things happen in the code.