Implement maintaining object relationship graph

For each object maintain parent-child relationship graph, i.e. list of
parent objects ('parents' property) and list of children objects ('children'
property).

Objects without parent(s) are objects specified in init manifest.
Objects without children are object of types that do not reuse other types.
Status Job ID Name Coverage
  Test
passed #8484
pycodestyle

00:00:15

passed #8483
shellcheck

00:00:18

passed #8485
unit_tests

00:00:21