Divij/client message flow

Wiring up application registration with client "init_interview" message.

For the time being we are hardcoding registered applications see line 52, 53 on interview.py. Registration via selection screen to follow.

PEP8 Compliant. Tested notes and heartbeat application.
so currently apps will be empty so onjoin wont get called. Before, we repush this can we add an onjoin to one of the apps that just prints onJoin called or something to ensure this is working.