made snipers unable to shoot anything else than infantry

fixes #3530 using a target type workaround
Add Order.ExtraData field.
Add ITargetableInfo interface for querying target types.
Change WeaponInfo.EffectivenessAgainst to take ActorInfo.
Introduce Target.Type property.
Merge IOrderTargeter.CanTargetActor and CanTargetLocation.
Allow world and (render-) player actors to render.
Use selection priority when picking tooltip actor.
Track per-player frozen actors.
Show tooltips for frozen actors.
Add FrozenActor target type.
Add plumbing for issuing orders against frozen actors.
Add helper for resolving orders against frozen actors.
Enable frozen order: Attack.
Enable frozen order: DeliverSupplies.
Enable frozen order: LegacyCaptureActor.
Enable frozen order: C4.
Enable frozen order: DemoAttack.
Enable frozen order: Captures.
Enable frozen order: EngineerRepair.