When aileron was copied from web2, old unread-messages styling lingered

This removes the square box with borders behind the "New Messages" box
which looks weirdly out of place on 4.0.  What's happening is that the
'box' on web2 is becoming a weird background box to the new title box css
showing up in aileron.
Make links in the "New Messages" popup show as links

Without this, it's really not obvious (unless you hover, or know) that
there are two embedded links you can click on.  Putting it in base/ so
that it works on aileron and web2.
Merge branch '4.0/unread-message-styling' into 4.0-trunk