Coloured icons for appointments

[Karl Lattimer]

We want to have coloured and probably contextual icons for the appointments in indicator datetime. However evolution currently returns null every time.

Code exists in the datetime service to do this job, however it has been untested as we can't get colours from evolution

[Aurélien Gâteau (agateau)]

Adding Ayatana-Design as they will probably want to provide feedback on the way appointments should be rendered.

[Karl Lattimer (karl-qdh)]

After using the generate instances method instead of get objects the sources started returning colours. I tidied up the code here in the attached branch and it works well.