Automatically create the Aphlict log directory

Summary: Fixes T6944. Attempt to automatically create the log directory for the Aphlict server. If the directory can't be created, throw a helpful exception.

Test Plan:

1. Set notification.log to /var/log/aphlict/aphlict.log.
2. Ran ./bin/aphlict debug and saw an exception (because the user doesn't have permissions to create the /var/log/aphlict directory).
3. Ran sudo chmod 777 /var/log.
4. Ran ./bin/aphlict debug and saw the /var/log/aphlict directory created.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Maniphest Tasks: T6944

Differential Revision: https://secure.phabricator.com/D11387