BACKLOG-1582 - Document interfaces mentioned in SSO doc

What was done:
1) added comments for the interfaces and classes mentioned in the SSO
documentation. The comments were grammar checked by Chantel.
Merge pull request #2180 from kolinus/BACKLOG-1582

BACKLOG-1582 - Document interfaces mentioned in SSO doc
[BACKLOG-1562] Add support for ACL shadow nodes in repository