Sync status reporting/ dashboard v1

Summary:
Relevant hackpad: https://inbox.hackpad.com/Mailsync-Status-06uPCwSkRaP

Redis server
------------
Our Redis server config file is etc/redis.conf.
The script to start the Redis server is bin/inbox-dashboard.

Redis client
------------
inbox.server.reporting implements the Redis client we use.
This has documentation on the information stored in Redis, schema used.

The script to bootstrap Redis on start-up is bin/bootstrap-dashboard.
We probably want to fold this into inbox-sync.

This revision includes mailsync code changes to update Redis as well.

Dashboard app
-------------
A basic Flask app is in inbox/monocle
To run it:
python inbox/monocle/app.py
go to http://0.0.0.0:5000/all or http://0.0.0.0:5000/{account_id}
NOTE: This app is still WIP.

This should probably live elsewhere, I'm happy to hear code organization thoughts.

Test Plan:
In progress.
Also, the app.

Reviewers: spang

Reviewed By: spang

Subscribers: emfree

Differential Revision: https://review.inboxapp.com/D182