Expose signed containers in the UI

[ssbarnea]

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• H) Container and content signing capabilities (depends on other team 2.2 deliverables) docs.google.com/document/d/1aGiEaYtQXa8H80zdHr-Fa3JXisCsN3xPH9HcHREmdCg/edit?usp=sharing

[ssbarnea]

I think that is related to https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux_atomic_host/7/html/managing_containers/signing_container_images -- but before doing anything in navigator, we first need to have the first creator-ee container signed.