Implemented set_date method, moving update of ::date attribute to another call
outside the construction process. The method can be used to set or update the
GcalView::active-date property
Implemented changes from GcalView API
Integrated GcalWeekView into application flow.
Added gcal_view_add_event method GcalView interface.
Fixed size_allocate implementation in GcalMonthView to allocate children events.
There's still work to be done here.