Add full support for 16, 32 and 64-bit Ints in Swift

And rework the Swift property type init in the process. Switch to enumerating
the Swift properties and building up an array of fake obj-c properties for
them, and using the obj-c code for the rest. This makes it possible to preserve
the size of integer properties (previously they were all just
RLMPropertyType.Int), and makes it possible to reuse the obj-c functionality
for things like RLMArray property element type validation and primary key
support, neither of which were previously implemented for Swift.

Add a dummy implementation of RLMSwiftSupport for Xcode 5 to eliminate most of
the `#if REALM_SWIFT` checks.