Replace Property with Type

[katmatt]

Our current ObjectType models its properties with a separate Property type. This isn't following the RAML spec which uses types for the properties. I had doubts in the beginning if I really liked to reuse Type for them, but with our experience now it seems to be better to remove our Property type and replace it with Type.

This change has a big impact on our codegenerator and updating to this fix will take some time.