[ui] use "Segoe UI" as default font on Vista and later

* Greatly improves the display of non western character sets, such as CJK.
* Note: Since I'm no longer willing to go the extra mile for XP, the way we
  handle the non availability of the Segoe font there is by doing the lazy
  thing and duplicating all our UI resources, in a similar way as what we do
  for RTL, and setting them with the old "MS Shell Dlg".
* Also update some Syslinux V5 refs to Syslinux V6.
* Closes #308