week-view: implement get_left/right_header methods

Add macro to include private instance data into GcalWeekView objects
week-view: modernize accessing private instance
week-view: remove navigation controls

This commit just remove the related code. We will make the view work
further along the way.
week-view: draw header updated
week-view: modernize Gobject boilerplate code
week-view: remove deprecated methods and warnings
event-widget: use single click activation

Use pointer cursor
week-view: fixed doc sections