Put most recent 20 messages in notif

otherwise we'll end up returning the wrong 20

Fixes https://github.com/vector-im/vector-web/issues/1648

Rewrite LDAP Authentication against ldap3

Use the pure-python ldap3 library, which eliminates the need for a
system dependency.

Offer both a `search` and `simple_bind` mode, for more sophisticated
ldap scenarios.
- `search` tries to find a matching DN within the `user_base` while
  employing the `user_filter`, then tries the bind when a single
  matching DN was found.
- `simple_bind` tries the bind against a specific DN by combining the
  localpart and `user_base`

Offer support for STARTTLS on a plain connection.

The configuration was changed to reflect these new possibilities.

Signed-off-by: Martin Weinelt <hexa@darmstadt.ccc.de>

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 the legacy v0 content upload API.

Fix substitution failure in mail template

The existing content can still be downloaded. The last upload to the
matrix.org server was in January 2015, so it is probably safe to remove
the upload API.

Linearize some federation endpoints based on (origin, room_id)

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.