Event Cleanup

[jmakowski1123]

• Implement changes from the documentation epic

• Ensure all events are explicitly versioned

• Ensure all changes are carried through xAPI / Caliper

[pomegranited]

@bmtcril

• If we use numeric versions (which I'm sure we would anyway), then we can indicate supported version ranges for our SQL queries.
• Should we use Clickhouse views to obfuscate xAPI schema version changes from Superset's datasets?

[bmtcril]

@pomegranited I think this is where dbt will eventually end up being our friend. Sometimes event versioning will be meaningful breaking changes that we'll want to look at separately and we should be able to split out by that, but where possible we could also combine them into one logical unit. I think in most cases our changes will be additive, in which case filtering by version may not be such an issue, some data just won't be there because we weren't collecting it yet and so probably wouldn't warrant a separate model.