Add plugin to init databases using flynn-postgres.

Design a init mechanism through which this can happen.
Support storing server urls in config file.
Start etcd with peerport.
Add support for delays while bootstrapping.
Setting the image manually was broken.
Fix missing dependencies.
Allow local variables in environment variables.
Start with two plugins that the future should bring.
Add a Dockerfile.

Ultimately, this is supposed to run in a container.