+ should show log messages not associated with a module

```
git clone git@github.com:eclipse-m2e/m2e-core.git
cd m2e-core/m2e-maven-runtime
mvnd clean install # still ok
cd ..
mvnd clean package -DskipTests
```

Now seemingly nothing happens, but `CRTL-B` reveals that there is an extension that does a lot of downloads, but no module is built yet, so the messages are no associated to any module.

In the threaded view, hitting `+` currently does not show the messages that are not assuciated with any module. I wonder whether we should those as well upon hitting `+`?

Reproduce the behavior with the commands in the issue, then use CRTL-B and the threaded view to inspect how unassociated log messages are handled when `+` is pressed. Done means pressing `+` also reveals messages produced before any module is built.

Written by the indexing model from the issue text.