FR: Add a 'currentTypeExists' query to the permissions endpoint

[kbrandwijk]

Now that reusability of permission queries has finally arrived with the new CLI beta, it would be great if you could reuse PQ's more easily by making them type-independent. I would like to have a CurrentTypeExists or NodeTypeExists or similar, that will take the current node type. That way, a 'only the owner' type PQ would be more easily reusable across many Types.

[marktani]

I love it! Closing as duplicate of #189.