Adding the todolist endpoints

[yoelhor]

Purpose

This PR:

1. Adds the .NET Core To do list endpoints, to align with other Azure AD B2C client samples. With this change the developer can choose between using the .NET core or node.js sample (todolist.js and index.js).
2. Adds a public endpoint which helps with the debugging process (index.js).
3. Fix CORS issues (index.js)
4. Change the app settings to validate the issuer name (config.json).

Does this introduce a breaking change?

[ ] Yes
[x] No

Pull Request Type

What kind of change does this Pull Request introduce?

[ ] Bugfix
[x ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[ ] Other... Please describe:

How to Test

Read the active-directory-aspnetcore-webapp-openidconnect-v2 guidance. Then change the Angular sample to use this endpoint (instead of the .NET Core one). The ToDoList endpoint URI can be found here.