Implement custom Appointment class

[ktaekwon000]

Original post:
When implementing the Appointment class for v1.3, consider using the interface given at jfxtras.scene.control.agenda.Agenda.Appointment (Javadoc) if suited for our application, as it may make integration into the calendar easier. A sample implementation by the developers of jfxtras jfxtras.scene.control.agenda.Agenda.AppointmentImpl can be found at Javadoc and code.
Check out the sample code at https://github.com/JFXtras/jfxtras/tree/10.0/jfxtras-agenda/src/test/java/jfxtras/scene/control/agenda/trial for integration between AppointmentImpl and Agenda.

Update 1:
I forgot about iCal integration while writing this issue. I'll rewrite this by this evening when I have a better idea of how to link the agenda library and the iCal APIs. I currently suspect I'll be using jfxtras-icalendaragenda and jfxtras-icalendarfx for the GUI and API respectively.

Update 2: (outdated)
I've tried changing the current implementation of Agenda into ICalendarAgenda but this causes many issues for some reason.
The primary issues with this occurring is that the calendar becomes editable if I use this class instead of Agenda, and the fact that editing is extremely buggy. (I had the app crash with a memory error as I was implementing this class)
I'll look for if I can integrate other APIs (Probably iCal4j?) into jfxtras-agenda but I think we'll end up using Agenda for the GUI in the end.

Latest update:
I managed to find a code snippet online that disables the mouse interaction with the ICalendarAgenda. Since the bug mentioned in update 2 is fixed now, I think we can base our implementations off ICalendarAgenda and icalendarfx.