Optionally start or stop workers in synctl.

Optionally start or stop an individual worker by passing -w with
the path to the worker config.
Optionally start or stop every worker and the main synapse by
passing -a with a path to a directory containing worker configs.

The "-w" is intended to be used to bounce individual workers proceses.
THe "-a" is intended for when you want to restart all the workers
simultaneuously, for example when performing database upgrades.

Remove registered_users from the distributor.

The only place that was observed was to set the profile. I've made it
so that the profile is set within store.register in the same transaction
that creates the user.

This required some slight changes to the registration code for upgrading
guest users, since it previously relied on the distributor swallowing errors
if the profile already existed.

Disable responding with canonical json for federation

Turn use_frozen_events off by default

Only re-sign our own events

Fix ``KeyError: 'msgtype'``. Use ``.get``

Fixes a key error where the mailer tried to get the ``msgtype`` of an
event that was missing a ``msgtype``.

```
 File "synapse/push/mailer.py", line 264, in get_notif_vars
 File "synapse/push/mailer.py", line 285, in get_message_vars
 File ".../frozendict/__init__.py", line 10, in __getitem__
    return self.__dict[key]
    KeyError: 'msgtype'
```

Inline the synchrotron and pusher configs into the main config

This means that the workers can override the event_cache_size
directly without clobbering the value in the main synapse config.

Fix TypeError in call to bcrypt.hashpw

Fix some `/preview_url` explosions

- At the very least, this TypeError caused logins to fail on my own
  running instance of Synapse, and the simple (explicit) UTF-8
  conversion resolved login errors for me.

Signed-off-by: Salvatore LaMendola <salvatore.lamendola@gmail.com>

Enable testing the synchrotron on jenkins

Linearize fetching of gaps on incoming events

This potentially stops the server from doing multiple requests for the
same data.

Work around TLS bug in twisted