mailu/webmails/roundcube
lub 02cfe326d3 support using files for SECRET_KEY and DB_PW
this enables usage of e.g. docker swarm secrets instead of exposing the
passwords directly via environment variables

just use DB_PW_FILE and SECRET_KEY_FILE instead of DB_PW and SECRET_KEY
..
Dockerfile update roundcube
config.inc.php support using files for SECRET_KEY and DB_PW
php.ini Dynamic attachment size
start.py Fix roundcube permissions, tail correct log