Using show_all is a pita, since it causes a bunch of bugs whenever we
need to conditionally show/hide widgets. This removes all uses on the
main window in favour of either just show() or present(), and ensures
that its widgets that are shown by default, are shown by default.
* Ported Gtk.Action to GLib.Action in the GearyController.
* Removed Gtk.AccelGroups (handled through Gtk.Application now).
* Got rid of Gtk.UiManager (now all is done through Gtk.Builder).
* Throw away workaround for conflicting Gtk.Actions in ComposerContainer.
* Aggregate zoom in/out/normal into one parameterized zoom action.
Signed-off-by: Niels De Graef <nielsdegraef@gmail.com>
