Implements sessions for Twilio integration

[buffolander]

It implements the concept of sessions for Twilio integration. – Session duration is configured as an env var in the Dockerfile – When not configured or omitted, the incoming phone number is used as session reference

Other minor changes:

• Moves the projectId configuration from each individual server to the Dockerfile
• Updates documentation on projectId configuration
• Cleans up unused code in ./twilio/server.js
• Minor auto-linting changes

[buffolander]

In the Twilio server, when you're simply replying to a message via res.send it's unnecessary to initialize Twilio with your accountSID and authToken