Fixing group content access

WIP
Following #196 and #185 we added tests to verify group content privacy is being kept, including with the c4m "restricted" option.
This was done via 2 patches:
OG - https://github.com/Gizra/og/pull/10 (still fails in og simpletest, needs to solve it).
pluggable_node_access - https://github.com/Gizra/pluggable_node_access/pull/14 (which depends on the OG patch above).

@HelenaEksler can you please change the branch so it would pick up your branch