Clone specific repositories as well

This will add a functionality to clone specific repositories
from ownCloud organization.

It also generates an error if the core environment is not set up.

To use: `python3 -m ocdev setup <repositoryname>`

The conditions for base and core are added because otherwise
the setup command could be used only once
Ok, sorry, read the whole file (god this diff is difficult to read) and you need an elif arguments.level not in ('base', 'core'):