Move node_access_strict logic into OgAccess

[pfrenssen]

Currently the node_access_strict logic is executed in og_entity_access(), meaning that it is not checked when the methods in OgAccess are called directly.

There are three public methods which currently return results which completely ignore this mechanism:

• OgAccess::userAccess() - not sure if it applies here, since this only deals with groups
• OgAccess::userAccessGroupContentEntityOperations() - this definitely needs it
• OgAccess::userAccessEntity() - this probably doesn't need it directly, since it delegates to ::userAccessGroupContentEntityOperations()