Introduce "dev environment" and dotenv

There are now two dockerfiles. One for production, one for development.
All configuration is now also handled through dotenv files,
which these dotenv files, as well as the included VSCode launch tasks
use.

.gitignore

@@ -137,4 +137,7 @@ data/
 node_modules/
 
 # Version identification file
-.version
+.version
+
+# Docker secrets
+secrets.yml