Updated documentation for the new validation model and restructured internals#3056

iNinja merged 24 commits intodevAzureAD/azure-activedirectory-identitymodel-extensions-for-dotnet:devfrom

iinglese/tidy-up-new-validation-modelAzureAD/azure-activedirectory-identitymodel-extensions-for-dotnet:iinglese/tidy-up-new-validation-modelCopy head branch name to clipboard