Allow workspace layout to be overridden

meta_workspace_manager_override_workspace_layout is implemented by calling meta_workspace_manager_update_workspace_layout which respects the workspace_layout_overridden flag. After the first call to meta_workspace_manager_override_workspace_layout all subsequent calls fail silently.

Reset workspace_layout_overridden to FALSE before calling meta_workspace_manager_update_workspace_layout.

Signed-off-by: Ron Yorston rmy@pobox.com