rather than passing an entire filter dict for every single syncs.
This shortens the request URL and prevents troubles with some servers
that have an absurdly low max URL length (e.g. halogen.city).
Previously, member events in initial syncs (unless user had "hide member
events" and "hide profile events" set to false in their config) were
completely discarded with the help of a sync filter, instead of simply
being hidden like events loaded from room backfilling.
This was done due to the common case of rooms getting only
userconfig-ignored/hidden events on startup (especially with the
low number of initial events requested for lazy initial sync),
and thus having nothing to show as "last message" in
the room list (room delegate subtitles).
Other problems resulted from this, like missing join/leave events
when the config was set to hide profile events but not other
member events, and the "Members not synced" (#54) in encrypted room
with recent discarded member events.
The discarding filter is no longer used. Instead, if a room in the room
list has no visible "last message" and is currently visible to the user,
messages will be lazily fetched until we find something adequate or the
room goes out of view.
Contact the server's .well-known API before anything to get
available login flows instead of blindly assuming it will be
m.login.password, and to get the server's real URL instead of
requiring users to remember that e.g. it's "chat.privacytools.io"
and not just "privacytools.io" despite user IDs making it look like so.
The server field will also now remember the last accepted URL.
While a user file write operation #1 was queued in the _write_loop,
it was possible meanwhile for another function to read the file
(the current old version on disk), add some data to it,
add submit the write (operation #2).
The modifications from operatio #1 were then completly lost at best.
