Activated signals should provide the action timestamp or platform data

[Marco Trevisan (Treviño)]

Scope::activate_uri and PreviewAction::activated should provide an extra parameter to pass to the lens the activation timestamp or some platform-data that the scope should use to call external applications with proper parameters that would, for example, allow to avoid that the Window Manager won't focus the just-opened window due to the focus-stealing-prevention mechanism.

This leads for example to bug #1164543.