Remove "support" for "Large desktops (>1200px)"

 - Bootstrap provides support for large desktops which I did not realise
 - when displayed in "large desktop mode" things don't look very good
   anyway, so instead of trying to tweak things to support it better I have
   decided just to remove support (limiting the content to a width of 940px)
 - as a result the bootstrap-responsive.css stuff is now included in
   bootstrap.css (due to how the Bootstrap "Customize & Download" works)