Provide access callback for log properties

A lot of the log properties defined in hook_entity_property_info_alter() have 'setter permission' => 'administer log module'.

This is causing issues when trying to create/update logs via the RESTful Web Services module API endpoint. Only users with the 'administer log module' permission are able to use the API to interact with Log entities.

A better approach would be to create an access callback for log properties which checks user-level permission to create or edit the log entity. Then we can remove 'setter permission' and add 'access callback' to use that instead.