Feat flowsheet middleware

[AyBruno]

Middleware used to block access to certain controllers based on DJ state

• checkActiveShow.ts contains logic to only continue on to further middleware iff there is a currently active show.
• checkShowMember.ts contains logic to only continue on to further middleware iff the requesting dj is a member of the current show. This function relies on the cognito middlware in order to work as it compares values located in the decoded token (which gets stored in res.locals) against our database. Because of this it is important that it is always called after cognitoMiddleware() in the chain of middeware. (sheesh I've typed middleware a lot here)

I've also included in app.ts a testing endpoint to demonstrate the usage of both of these middleware functions.