Fix 'make check' after Gtk::Misc has been deprecated

* examples/book/assistant/examplewindow.cc
* examples/book/box/examplewindow.cc:
* examples/book/custom/custom_container/examplewindow.cc:
* examples/book/headerbar/examplewindow.cc:
* examples/book/placessidebar/examplewindow.cc:
* examples/book/searchbar/examplewindow.cc:
* examples/book/spinbutton/examplewindow.cc: Don't use deprecated
Misc::set_alignment() and deprecated Label ctor.