[bugfixes] fixed thread-locking bug for face wrapper

- implemented RAII for accessing a face in the face wrapper class
[untracked] added session initialization method
[bugfixes] thread-level memory content cache

- now each publishing stream creates designated memory content cache
for each newly created thread; upon thread removal content cache is
destroyed and all registered prefixes get unregistered - this ensures
on interest callbacks will never be called for deallocated objects