sources: Changes in related contents management. - Remove `getParentGroup` method, use related contents instead. - Return only a single group when asked for the parent.

cov-core==1.15.0
coverage==4.0.3
invoke==0.12.2
mock==1.0.1
pytest==2.8.7
pytest-cov==2.2.1
pytest-mock==0.10.1