added order in daily planning based on officeAvailability which considers holidays, extra_availabilities, general appointments from Appointment, and subject assesments from AppointmentTypeLink

Avoid possibility to change the worker when adding holidays or extra availabilities. Changed the header

removed appointments reference from model. Filter out extra availabilities for the method is_on_leave

moved function to utils.py (future code will also need the midnight function) and added utils module

Fixes 204. Not sure if it's the best solution but it makes sense to call the web.views.workers the same way it's done in the sidebar