Properly unbind property: Bug #734487

Use BaseObject.unbind_property() until Vala 0.26 is minimum, where
Binding.unbind() is bound.
Update .doap file
Add calendar in Calendar Manager: Bug #733637

This also removes the "Add Calendar..." item from the application
menu, leaving just "Calendars" to launch the Calendar Manager.
Merge branch 'master' into wip/732029-gtk-312

Conflicts:
	src/activator/activator-window.vala
	src/toolkit/toolkit-entry-clear-text-connector.vala