Attempting to use GMenu with GtkBuilder
More use of GMenu with GtkBuilder
More use of GMenu with GtkBuilder

gmenu: Adapt to improved Gio::Action API.
Refactor: Move GlomBakery::AppWindow_WithDoc_Gtk into Glom::AppWindow.

We no longer need the Bakery abstractions and it just complicates
the code, leaving lots of code that is never called.
Refactor: Remove init_toolbars()

We don't have any toolbars.
Refactor: Merge the UIManager ui descriptions

We do not need the higher-level placeholders now that the menu is
all built in the same class.
Refactor: Remove unused AppWindow::get_ui_manager().
gmenu: More conversion to Gio::Menu

Convert the main menu, and some of the context menus.
gmenu: LayoutWidgetUtils: Replace UIManager
gmenu: Print Layout: Replace UIManager
gmenu: AddDel: Replace UIManager.
gmenu: NotebookLabelGlom: Replace UIManager
gmenu: Move the main menu into the .glade file.

* glom/appwindow.[h|cc]: Move the GMenu XML into:
* ui/operator/window_main.glade
  and use it from the regular Gtk::Builder instance.

The GMenu XML needs to be in a separate file so that
its human-readable parts can be translated.

However, glade does not seem to support GMenu yet,
so we cannot edit this file inside glade.
Replace deprecated H/V widgets in glade files.
gmenu: Print Layouts: Fix Show Outlines
gmenu: move Relationships Overview menu to .glade file.
Glade files: Update required GTK+ versions
Glade files: Remove unnecessary gtksourceview requirements.

* ui/developer/*.glade:
  Remove  <!-- interface-requires gtksourceview 0.0 -->
  from files that do not really need GtkSourceView.
gmenu: Move Print Layout context menu into .glade file
gmenu: Relationships Overview: Move context menu into .glade file