Replaces DEFAULT_ROOM_VERSION constant with a method that first checks the config, then returns a hardcoded value if the option is not present.

That hardcoded value is now located in the server.py config file.

Rather than have three methods which have to have the same interface,
factor out a separate interface which is provided by three implementations.

I find it easier to grok the code this way.

This is a first step to checking that the key is valid at the required moment.

The idea here is that, rather than passing VerifyKey objects in and out of the
storage layer, we instead pass FetchKeyResult objects, which simply wrap the
VerifyKey and add a valid_until_ts field.

* Pass time_added_ms into process_v2_response

* Simplify process_v2_response

We can merge old_verify_keys into verify_keys, and reduce the number of dicts
flying around.

These were never used, and poking arbitary data into objects from other
packages seems confusing at best.

Storing server keys hammered the database a bit. This replaces the
implementation which stored a single key, with one which can do many updates at
once.

I was staring at this function trying to figure out wtf it was actually
doing. This is (hopefully) a non-functional refactor which makes it a bit
clearer.

requests 2.22.0 as been released supporting urllib3 1.25.2

Signed-off-by: Marcus Hoffmann <bubu@bubu1.eu>

* expose SlavedProfileStore to ClientReaderSlavedStore

Implements https://github.com/matrix-org/matrix-doc/pull/2002.

When considering the candidates to be forward-extremities, we must exclude soft
failures.

Hopefully fixes #5090.

* Pin eliot to <1.8 on python 3.5.2

Fixes https://github.com/matrix-org/synapse/issues/5199

* Add support for 'markers' to python_dependencies

* tell xargs not to strip quotes

If we remove support for a particular room version, we should behave more
gracefully. This should make client requests fail with a 400 rather than a 500,
and will ignore individiual PDUs in a federation transaction, rather than the
whole transaction.

This reverts commit ce5bcefc.

This caused:

```
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/local/lib/python3.7/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/home/synapse/src/synapse/app/client_reader.py", line 32, in <module>
    from synapse.replication.slave.storage import SlavedProfileStore
ImportError: cannot import name 'SlavedProfileStore' from 'synapse.replication.slave.storage' (/home/synapse/src/synapse/replication/slave/storage/__init__.py)
error starting synapse.app.client_reader('/home/synapse/config/workers/client_reader.yaml') (exit code: 1); see above for logs
```

Implements MSC1884

* fix mapping of return values for get_or_register_3pid_guest

* expose SlavedProfileStore to ClientReaderSlavedStore

* Stop telling people to install the optional dependencies.

They're optional.

Also update the postgres docs a bit for clarity(?)