As we cannot style the navigation elements freely with the restricted
version of CSS that QTextBrowser supports, we need to inject
separator elements between the prev/next page links.

This change adds a 'bullet' character wrapped in a <span> as a
separator. A rule is added to the standard offline CSS to hide the
separator as it's not needed there.

Change-Id: I13220a2a60e2d3063f94bc7dff0e4320d0bed4f6
Reviewed-by: Martin Smith <martin.smith@digia.com>