Improvements for c-sharp service generation

[markcowl]

This encompasses some simple improvements to the c-sharp emitter

• Add exception types for spec error messages
• Add error configuration that translates specific errors into responses with appropriate http status codes
• Improve naming of anonymous types using context
  • Inline parameters using operation name
  • Inline properties using model + proprerty name
  • Inline responses using operation +'Response'
• Keep a central cache of emitted type names to prevent low probability generated name clashes

est: 5