Moved Scaffolding to its own solution with modifications

[systemlibrary]

NOTE: I've not looked carefully at the build/publish mechanism this repo uses, but most likely a path to scaffolding.csproj needs a change as its moved inside a 'Scaffolding' folder

• Refactored and restructured the Scaffolding tool into various classes and its own solution file (.sln)
• Added option to generate all outputs into a single file through "-f" argument
• Prefixing C# keywords that are used as prop or types in the schema, resulting in those keywords getting a prefix @
• Added a test project to test some input scenarios and (partially) verify the output of the tool
• Supports reading a local json file as the schema, additionally to querying the graphql endpoint
• Supports adding basic auth headers for the Introspection Query
• Supports adding other custom headers and values for the Introspection Query
• Added options to save the schema.json file if one wants to view it, the json that Introspection Query returned
• Added option to export the query this tool uses to grab the schema.json file, if one cannot get this tool to run against the graphql server for some reason, but one have access to the graphql server and its playground, one can manually run it to get the json schema
• 'private' and 'readonly' keywords are omitted in C# and scaffolding tool
• Updated readme and readme-nuget
• Added a simple test project to test the tool (.exe) generated