From v0.2 to v0.3

In v0.1 and v0.2, there were two different backend services; one to serve the JSON API, and one to serve the web interface.

In v0.3, these have been consolidated into a single server. This means that you no longer need a compose file with two service entries. Except for STORYTELLER_API_HOST, all environment variables that were supported in v0.2 are still supported, and can be placed on the single new compose service. The image for this service should be registry.gitlab.com/storyteller-platform/storyteller:latest for CPU-only instances, or registry.gitlab.com/storyteller-platform/storyteller:cuda-latest for CUDA-enabled instances.