Matrix-appservice-irc: Handle registered-user-only rooms better

[ara4n]

We have mass confusion in ##linux on FN, which quiets unregistered users by default. At least we should show error messages inband in the room - but critically not make it look as if messages have sent correctly in the first place. Unsure on how best to do that. We should also make it clearer how to register with NickServ

[ara4n]

See https://riot.im/app/#/room/#matrix:matrix.org/$1477173400974644OjfLn:matrix.org for the full story.

[lukebarnard1]

How about showing a notice in band like, "Unable to send message to channel, have you signed in with NickServ? Talk to @freenode_NickServ:matrix.org to register." ?

Alternatively, I suppose this would be fixed when m.bots.errors etc. is introduced

[Matrixcoffee]

This bug is missing a priority label.

[dimm0]

Can't join the #linux channel, is it still the issue?

[grahamperrin]

err_needreggednick

Note to self, because I aimed to help someone join (after seeing them repeatedly kicked), but couldn't remember where to find the help:

1. https://element.io/help
2. https://community.kde.org/Matrix#How_do_I_join_an_IRC_channel_that_requires_registered_nicknames.3F
3. https://community.parrotsec.org/t/trying-to-join-parrot-on-matrix-instant-kick/14554/2 ▶
4. https://github.com/matrix-org/matrix-appservice-irc/wiki/End-user-FAQ#i-am-getting-kicked-out-of-a-bridged-room-with-the--err_needreggednick-error
5. https://github.com/vector-im/element-web/issues/4090

(1) is not a Matrix issue, but as a non-starter it was frustrating in that IMHO (selfishly?) it could benefit from a link to https://matrix.to/ https://matrix.org/clients/ or anywhere that might have dropped a hint/reminder that there exists a wiki.

For the user who had difficulty, I offered (2) the KDE-provided content.

Later rediscovery of the Matrix wiki content was through the Parrot page.

Generally

unfuck-google (extension for Firefox) was my friend.