Provide entity type metadata for execute action

For a good rules user experience we must provide metadata for execute action.
Meaning: efq-execute mus not return list but (say) list.
This can be done in 2 ways:
1) If rules allows this, we can provide one action and attach metadata assertion in some suitable way. I filed #2103079: Allow providing Rules metadata assertions for lists of entities to get to know this. Alternately we can try and imitate rules_condition_entity_is_of_type_assertions() and just see if it works but i did not get to do that (i'm mainly offline the next 10 days).
2) We iterate over all entity types in hook_action_info() and provide one action per entity type. This has a minor drawback that it clutters up the actions list but we can do it right now without further info so i think we should just go for this. I started this in the "metadata" branch.