So Anjal can override what it needs to for its own purpose.
Also makes the EShellWindow design a little cleaner.
Methods added:
GtkWidget * (*construct_menubar) (EShellWindow *shell_window);
GtkWidget * (*construct_toolbar) (EShellWindow *shell_window);
GtkWidget * (*construct_sidebar) (EShellWindow *shell_window);
GtkWidget * (*construct_content) (EShellWindow *shell_window);
GtkWidget * (*construct_taskbar) (EShellWindow *shell_window);
EShellView * (*create_shell_view) (EShellWindow *shell_window,
const gchar *view_name);
Also added some new GObject properties to help decouple actions from
internal EShellWindow widgets created by these methods:
EShellWindow:sidebar-visible
EShellWindow:switcher-visible
EShellWindow:taskbar-visible
EShellWindow:toolbar-visible
