Implement account-notify, extended-join and WHOX

Also integrate it with NickAuth.

Closes #778.
Fix tests
Fix typo
Fix previous commit
Add do352 back for IRCds which do not support WHOX
Fix code style
Re-add removed comment
NickAuth: Don't clear auth when joining unidentified
Merge pull request #804 from nyuszika7h/account-notify

Implement account-notify, extended-join and WHOX
RSS: Remove use of deprecated property. Closes GH-807.
Dunno: Log commands. Closes GH-798.
Factoids: Fix compatibility of web server with Python 3. Closes GH-784.
Simplify and fix logic of umodes filtering. Closes GH-719.
RSS: Display nice error if an announced feed does not exist.