With lockdown settings available through GSettings, widgets can handle
lockdown integration themselves without having to use EShellSettings.
Also fixed a few places where printing or save-to-disk actions were
either not properly wired up or not responding to lockdown settings,
but much more work needs done. Attachments, for example, are not
honoring the disable-save-to-disk setting at all.
This too requires the recently-added gsettings-desktop-schemas
dependency.