The additional complexity is needed to allow at the same time:

  - Elements that are either in 'usb' or clone 'scenario'.
  - Elements that are specific to an OS.
  - QR codes and URLs that are specific to a single scenario.
  - Bits that are common to several OS but not all.

We also have to distinguish between <span> and <a> which are "inline"
and <div>, <img>, and <p> which are "block" because the "initial" value
of the "display" property is not available on IE.

See http://www.w3schools.com/cssref/css_initial.asp

Conflicts:
	wiki/src/install/debian/clone.mdwn
	wiki/src/install/inc/steps/switch.inline.mdwn
	wiki/src/install/inc/stylesheets/usb.css
	wiki/src/install/linux/clone.mdwn
	wiki/src/install/linux/usb.mdwn
	wiki/src/install/mac/usb.mdwn
	wiki/src/install/win/clone.mdwn
	wiki/src/install/win/usb.mdwn