Previously, there was a bug where a failed message would only show the
`.message_failed` icons on hover, the intent was for them to always be
visible if a message failed to send.
The cause of the above bug was that in
e7b1de8ace we modified the html
structure of the icons such that each icon was inside its own div,
which possessed the `message_control_button` class, and both such divs
were inside a `.message_failed` div. The unintended consequence of this
change was that the rule `.message_controls .message_control_button`
would apply `visibility: hidden` to the icons.
Hence, this commit explicitly sets the visibility of
`.message_failed .message_control_button` to `inherit`.
bc3d03730f