Support authenticated SMTP

Fix up federation SendQueue and document types

Speed up get_current_state_ids

Using _simple_select_list is fairly expensive for functions that return
a lot of rows and/or get called a lot. (This is because it carefully
constructs a list of dicts).

get_current_state_ids gets called a lot on startup and e.g. when the IRC
bridge decided to send tonnes of joins/leaves (as it invalidates the
cache). We therefore replace it with a custon txn function that builds
up the final result dict without building up and intermediate
representation.

fix typo in synctl help

Don't double encode replication data

Reduce rate of USER_SYNC repl commands

Closes (SYN-714) #1385

Signed-off-by: Daniel Dent <matrixcontrib@contactdaniel.net>

Rearrange TCP replication metrics

Move to using TCP replication

Deduplicate new deviceinbox rows for replication