Move Python files to an src/ folder

[KevinGDialpad]

Now that there are two source files, it makes it very visible that the root of this repo is messy.

Let's move content_converter.py and wiki_sync.py into an src/ folder.

I'd still copy them to the repo root in the Dockerfile, so the script can still assume that paths from repo root are also paths relative to the script. In other words, I don't have re-introduce the complexity that 75e259f removed.