This is mainly done by moving the calculation of where to send presence
updates from the presence handler to the transaction queue, so we only
need to send the presence event (and not the destinations) across the
replication connection. Before we were duplicating by sending the full
state across once per destination.

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