Restructure project

We previously didn't really had any structure in our project apart
from creating a new folder for each package in our project root.
Now that we have accumulated some packages, we use the well-known
Golang project layout in order to clearly communicate our intent
with packages. See https://github.com/golang-standards/project-layout

Dockerfile

@@ -1,8 +0,0 @@
-FROM alpine:latest
-
-RUN adduser --disabled-password api
-USER api
-COPY poseidon /home/api/
-
-EXPOSE 7200
-CMD ["/home/api/poseidon"]