lint: straightforward lint fixes in dnf.cli.output.
cleanup: imports in dnf.cli.output
cosmetic: use classmethod as a decorator in config.py.
fix: pluginconfpath is a list.
packaging: own /etc/dnf/plugins. (RhBug:1118178)
Ship /usr/bin/dnf-3 to run DNF under Py3. (RhBug:1117678)
packaging: python3-dnf depends on dnf. (RhBug:1119032)

This prevents conflicts when the two packages are not upgraded in
lockstep. Alos we don't have to package /etc, locales etc. twice then.
depsolving: doesn't install both architectures of pkg by filename (RhBug:1100946)