Allow to lift arbitrary entities
Add Lua methods to allow to lift any entity.
By default, destructibles should be liftable depending on their weight property.
Built-in bombs should be liftable as well by default. For compatibility reasons, by default, NPCs with sprite
'entities/sign' should also be liftable.
destructible:get/set_weight()available to all entities, not only destructibles.
Make sure bombs are liftable by default.
Make sure NPCs with sprite
entities/signare liftable by default.