Add b prefixes to some strings that are bytes in py3

Replace old-style raise with six.reraise

Return 401 for invalid access_token on logout

use python3-compatible prints

Replace some type checks with six type checks

Improve handling of SRV records for federation connections

update prometheus dashboard to use new metric names

Return a 404 rather than a 500 on rejoining empty rooms

We aren't ready to release this yet, so I'm reverting it for now.

This reverts commit d1679a4e, reversing
changes made to e089100c.

Filter ourselves out of the server list before checking for an empty remote
host list, to fix 500 error

Fixes #2141

Signed-off-by: Adrian Tschira <nota@notafile.com>

The old style raise is invalid syntax in python3. As noted in the docs,
this adds one more frame in the traceback, but I think this is
acceptable:

    <ipython-input-7-bcc5cba3de3f> in <module>()
         16     except:
         17         pass
    ---> 18     six.reraise(*x)

    /usr/lib/python3.6/site-packages/six.py in reraise(tp, value, tb)
        691             if value.__traceback__ is not tb:
        692                 raise value.with_traceback(tb)
    --> 693             raise value
        694         finally:
        695             value = None

    <ipython-input-7-bcc5cba3de3f> in <module>()
          9
         10 try:
    ---> 11     x()
         12 except:
         13     x = sys.exc_info()

Also note that this uses six, which is not formally a dependency yet,
but is included indirectly since most packages depend on it.

Signed-off-by: Adrian Tschira <nota@notafile.com>

Implement group join API

Add response size metrics

postgres port script: fix state_groups_pkey error

as opposed to join_policy, which is really only pertinent to the
synapse implementation of the group server.

By doing this we keep the group server concept extensible by
allowing arbitrarily complex rules for deciding whether a group
is openly joinable.

Fixes https://github.com/matrix-org/synapse/issues/3050.

Improve logging and comments. Group all the stuff to do with inspecting tables
together rather than creating the port tables in the middle.

We really shouldn't spit out "Failed to create port table", it looks scary.

use PUT instead of POST for federating groups/m.join_policy

Add a blurb explaining the main synapse worker

Add room_id to the response of `rooms/{roomId}/join`