…ositories with the "plain" suffix

I.e. I (or a user) would want to add something like "spring-plain".
We should not confuse it with an actual "plain" repository!

Part of #365

… multi-file tasks

Part of #365

Part of #365

… avoid having to update the interface every time

Part of #365

… task so it may be overwritten

Part of #365

…sitory configuration

Part of #365

…tests for Spring Boot actually spin up Spring Boot

Part of #365