Add ability to use custom skin

docker-compose.yml

@@ -75,6 +75,7 @@ services:
 
     volumes:
       - ${DATA_ROOT:-/opt/eternitymail}/roundcube-config:/var/roundcube/config:ro
+      - ${ROUNDCUBE_SKIN_PATH:-../ep-roundcube-skin/eternity}:/var/www/html/skins/${ROUNDCUBE_SKIN_NAME:-eternity}:ro
 
     environment:
       ROUNDCUBEMAIL_DB_TYPE: mysql
@@ -94,7 +95,7 @@ services:
 
       ROUNDCUBEMAIL_USERNAME_DOMAIN: ${MAIL_DOMAIN}
 
-      ROUNDCUBEMAIL_SKIN: elastic
+      ROUNDCUBEMAIL_SKIN: ${ROUNDCUBE_SKIN_NAME:-eternity}
       ROUNDCUBEMAIL_PLUGINS: archive,zipdownload,newmail_notifier
       ROUNDCUBEMAIL_UPLOAD_MAX_FILESIZE: 50M