Use a conventional repository layout for esap-api-gateway

esap-api-gateway has a slightly surprising layout for its repository: the root directory contains almost nothing but an esap directory, which is a Python package (ie, it contains an __init__.py file), but also contains a bunch of static assets (esap/configuration_assets), a Dockerfile (esap/Dockerfile), some logs (esap/logs/esap.log -- why are we versioning logs?!), a variety of different types of configuration (SQLite databases, Python code, etc, in esap/esap), information on dependencies (esap/requirements), and a bunch of additional Docker configuration (in esap/docker, including esap/docker/ska — despite the name! — is marked as being not specific to SKA).

It would be nice to rationalize this. In particular, we should:

• Not mix configuration and assets with code;
• Not version logs at all;
• Move the docker-compose stuff into a separate repository, since it isn't really part of esap-api-gateway;
• Probably some other stuff.