Create TagHelper specific C# code Generation.

- Added TagHelperChunk generation.
- Added CSharp visitors to understand TagHelperChunk's and render corresponding C# code.
- Refactored some code in the CSharpCodeVisitor so it could be utilized in other classes.

#72 

I split up the test portion of this PR to reduce noise.  PR: https://github.com/aspnet/Razor/pull/135
We need a generic property visitor which generates properties in the generated C# class.  That's what this accomplishes.  Had to add some more to this guy in my code review addresses to make writing activatable properties easier.