Get rid of elixir_uuid and other compile warnings, support prefix

[dvic]

This PR contains:

• replace elixir_uuid with vendored version
• fix compile warnings
• support configuring a database prefix
• assign the inserted audit struct to the pipeline for further processing

[drteeth]

@dvic looks like some decent stuff in here, but it's all together. Would you mind picking it a part into separate PRs that can be considered on their own?

I see:

• mix import vs config updates
• compile_env vs get_env
• something to do with prefixing
• something with the pipeline
• UUID vendoring - maybe some quick explaination about why we want this