first draft of fitness module, with just body-type-measurement for now.

We're using `createdAt` and `updatedAt` in other places. Not at least, because it's actually date and time and `dateTimeCreated` works even less. :)

In any case, are you actually using underscores in the other modules? Pretty sure we're usually using lowercaseCamelCase everywhere, because that's kind of a common thing people do in JS. Maybe these are relics from copying the IDs from the dropdown form configuration from the Gym App one-to-one?