chanfeed: Add archive check during feed run

[nazunalika]

During feed check and build, the thread should be checked for archive or 404 status. If the thread is archived or 404 (in the case of some boards that may not archive), a message should be sent to the channel and the feed removed from rotation automatically without user intervention.

This will require a configuration change that will modify the dict used in the settings.json which may affect current feeds. This is an unknown.