Make ketamine craftable and change its metabolisation rate

[UrsulaMejor]

I'd be OK with this, but it would have to be a secret chem. We might want to rename ketamine while we are at it. Something goofy like somnium.

technically, it's still called something like sombutril or somnambutril in the code, the only thing cogs changed during the chem de-magickifying was the name :p