Consistently call the service "Pulp"

[evgeni]

We introduced the "Pulpcore" naming to differentiate between Pulp2 ("Pulp") and Pulp3 ("Pulpcore"), but the use of the wording is not consistent across the app and now that Pulp2 is gone we could go back to calling it "Pulp" everywhere.

Originally posted by @ehelms in #856 (comment)