Doing DOM operations in finally would cause them to happen even when the request was a failure. Consequence of these DOM operations would be new request, which would also end up in a 404, and so on.
This commit simply moves the DOM operations in the then block where it should be safe to make.
This is a followup of the previous refactor where we created two new
models to handle all the dedicated logic that was present in the
`ChatChannel` model.
For the sake of consistency, `DMChannel` has been renamed to
`DirectMessageChannel` and the previous `DirectMessageChannel` model is
now named `DirectMessage`. This should help reasoning about direct
messages.
