Clean up ./inbox.
Clean up ./inbox.

Here are the changes:
* Don't explicitly check for --email-address argument; we can make it a
  required argument and then argparse will spit out the right help
  message automatically.
* I want the auth command to also create a new account in the database
  for testing purposes.
* So far we've been naming all functions in this file directly after the
  subcommand, so let's continue doing that with add.
* Adapt for changes to oauth.py.

PriviPK/privipk-sync-engine,wakermahmud/sync-engine,nylas/sync-engine,ErinCall/sync-engine,PriviPK/privipk-sync-engine,closeio/nylas,EthanBlackburn/sync-engine,Eagles2F/sync-engine,closeio/nylas,nylas/sync-engine,Eagles2F/sync-engine,ErinCall/sync-engine,ErinCall/sync-engine,rmasters/inbox,jobscore/sync-engine,jobscore/sync-engine,gale320/sync-engine,jobscore/sync-engine,gale320/sync-engine,wakermahmud/sync-engine,rmasters/inbox,wakermahmud/sync-engine,ErinCall/sync-engine,rmasters/inbox,nylas/sync-engine,wakermahmud/sync-engine,ErinCall/sync-engine,EthanBlackburn/sync-engine,nylas/sync-engine,jobscore/sync-engine,closeio/nylas,gale320/sync-engine,Eagles2F/sync-engine,PriviPK/privipk-sync-engine,EthanBlackburn/sync-engine,wakermahmud/sync-engine,PriviPK/privipk-sync-engine,Eagles2F/sync-engine,rmasters/inbox,EthanBlackburn/sync-engine,gale320/sync-engine,gale320/sync-engine,PriviPK/privipk-sync-engine,Eagles2F/sync-engine,closeio/nylas,EthanBlackburn/sync-engine