More verbose debug logging

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Teach the NarManager about remote repositories

This tells the NarManager to look for nar attachments in remote
repositories before looking into local repositories. Previously we only
looked locally unless we were downloading dependencies explicitly.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Do not look in remote repositories twice

Earlier, downloading attachments was a special case: it was the only
part of maven-nar-plugin that would look at remote repositories. But
we're now looking into remote repositories by default, so the special
download case looked at the remote repositories twice.

We cannot remove the method NarManager#downloadAttachedNars(List,
List, ArtifactResolver, String), however, because it is part of the
public API of the maven-nar-plugin.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>