That way we don't lose the user's input values, we avoid flashing and we
avoid unnecessary rendering.
In the process, fixed an annoying issue where Chrome auto-completes
what it thinks is the username into the "Language Tag" field of the MUC
config form.
Instead we tell Chrome that the MUC JID is the username, thereby also
letting it save the password to to that JID.
Instead of padding the container, pad individual elements that need it.
This enables us to have highlighting (e.g. on hover) that spans the full
width of the controlbox.
updates #1069
