edit dialog: reworked ui, implemented composite widget
Merge branch 'week-view' into backend-improvements

Conflicts:
	data/ui/edit-dialog.ui
manager: added 'sync-start' and 'sync-end' signals

When the event is added into an online account, EDS syncs it. It is really important to provide this information feedback to the user
new event widget: inactivate read-only calendars
date entry: fix wrong month selection on calendar popover