Track subtype by name, not just index

[blowfishpro]

Useful to be able to re-order subtypes without breaking craft. Determining the subtype would go like this:

• If name is present, find subtype with that name
• If name is blank or invalid, fall back to index
• If index is invalid, set to zero.

Index would be something like -1 to begin with.

Should also add a uniqueness constraint on subtype names.