AccessControl class and CLog as Dict.
I changed the store_file_log function, and added an AccessControl class to client_classes. The motivation for this is that ClientLogs are now going to be represented as dictionaries. My thinking is that it'll have an "owner" key and "users" key. The "owner" key will correspond to a value that is of type AccessControl. (This corresponds to the encrypted key block idea in Sirius before the encryption). And the "users" key will have value of type list of AccessControl objects. That is, the list will contain AccessControl objects for each user with which the file is shared. Currently create_file will be broken because I commented out store_file_log, as I didn't know what arguments to pass in to  the newly changed store_file_log.