[2.0] Make Operations more magical

[robertmclaws]

In Version 2, I want Operations to feel like pure magic. When you tag a method, the ModelBuilder should automatically find it, register the types if they haven't been seen yet, looping through all the supported annotations and so forth, and appear in the proper location.

You shouldn't have to take over model building to register ComplexTypes, you shouldn't be confused about what HTTP methods it supports, and you shouldn't be surprised where it shows up in the model.

Should fix the following issues:

• [2.0] OperationAttribute + ModelBuilder.Action = identical model entries #652
• [2.0] OperationModelBuilder does not register complex types #651
• [2.0] Optional Parameters in Operations #656