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
Basically just added the `GeneratedTagHelperRenderingContext` to this guy, while I was at it I touched up some of the inconsistencies with how we do code now.  If you don't like the noise I can undo the changes.