Support for “Uses Scalar Type”.

[rokgregoric]

Summary of Changes

The Uses Scalar Type checkbox was not handled and therefore when using a swift template the generated output was wrong. Instead of using scalars it was always generated as NSNumber.

Now it mimics the behaviour of the Xcode generator.

Because the usesScalarValueType is not (yet) available on NSAttributeDescription I used a userInfo entry to pass the value around.

[rentzsch]

Hey Rok, this is an interesting Pull Request. Well done!

Also @atomicbird: momcom saves the day yet again.

[radianttap]

I was just looking into adding this as well, great work Rok.

Built from source and in my initial testing, it seems to work just fine.

[djbe]

Bit late since it's already merged, but:
Is there a reason why optional scalars are not supported? According to this it should be possible.

Also, why use implicitly unwrapped optionals if an attribute isn't an optional? In swift 3 the behaviour of these changed quite a bit.

[rokgregoric]

Xcode handles that the same way. It doesnt generate optional scalars. I am exacly sure right now. Tried a lot of options and that seamed the best.