Use enums for viewer and conversion status constants

[interim17]

What needs to happen?

Convert some types and constants to enums

Why should we do this?

During review on autoconersion, @ShrimpCryptid pointed out that it would be efficient and readable to use an enum where we currently use types in some cases, notably viewer status and conversionStatus. When converting these, we should also check for other opportunities to include legibility and efficiency of typing in the website repo.

When does this need to get done?

Not urgent, appropriate to fold into auto-conversion work