There was an issue with channel archiving, where at times the topic
creation could fail which left the archive in a bad state, as read-only
instead of archived. This commit does several things:
* Changes the ChatChannelArchiveService to validate the topic being
created first and if it is not valid report the topic creation errors
in the PM we send to the user
* Changes the UI message in the channel with the archive status to reflect
that topic creation failed
* Validate the new topic when starting the archive process from the UI,
and show the validation errors to the user straight away instead of
creating the archive record and starting the process
This also fixes another issue in the discourse_dev config which was
failing because YAML parsing does not enable all classes by default now,
which was making the seeding rake task for chat fail.
