DataManager: return empty list when account has no repos
When an account has not repos, the user should get info about it
in the GUI.
Currently, the DataManager returns null in that case, and then the
GUI display message about error fetching repos.
So change the DataManager to return empty list of repos in this case,
and then the GUI displays message that there are no libraries yet.
Merge pull request #85 from alfh/bug_account_without_repos

DataManager: return empty list when account has no repos