Roslyn refactorings and code actions

A refactoring (Ctrl + .) which allows you to:

1. when on Class declaration: * extract a class into its own file using current folder * extract a class into its own file using namespace based folder
2. when on Namespace declaration: * fix namespace to be folder based * rename file to any class declaration using current folder * rename file to any class declaration using namespace based folder
3. when on constructor parameter: * initialize a private readonly field named _{parameterName} with the following rules:
   • field existance is detected so no duplicated fields are generated
   • fields are generated with the same order of parameters
   • fields assignments are generated with the same order of parameters