SpringAtom -> #44

Calendar updated:
- SVAppointmentController.java is able to receive the request for the SAppointment.java in given date range
- StringToUnixTimestampConverter.java converts passed String value (UNIX timestamp) to bean UnixTimestamp.java which hold DateTime object
- added property which means: *retrieve events only for currently logged user* / if user is not logged (hence principal is anonymous) exception will be thrown
- CalendarEvent.java is simple bean (Hetoas driven) which is sent to the client and which contains references to data associated with given SAppointment as hyperlinks available further in the UI
due to class removal SAppointmentDTO
SpringAtom - #36

- initial domain object SCalendar which describes business object of an calendar
- calendars will be used instead of the SUser in the SAppointment to describe association
- user will be permitted to have more than one calendar