Int32 / Int64 should be a default type

[davidcorry]

I needed to explicitly store a 64-bit Int on 32-bit devices, but Pantry doesn't support Int64 by default. Including this line seems to work:

extension Int64: StorableDefaultType {}

(Hopefully there's no reason not to do that, it seems to work without error.)

Presumably Int32 also needs to be added, but I didn't explicitly test for that.