* add Option to specify Production vs. Sandbox Environment
also fixes issue
https://github.com/TerribleDev/OwinOAuthProviders/issues/54
* ability to specify Production vs. Sandbox environment per auth session in addition to global setting
* add examples to show usage of new Production vs. Sandbox Option for Salesforce provider
* initial commit for Typeform provider
* add Typeform project to solution
* use GUID for UserId and add warning regaring use for authentication