WebStyle: fix header module box CSS style
WebStyle: fix header module box CSS style

* Updated 'headermodulebox' class to fix display of the main menu
  tabs for some versions of Firefox.  (E.g. Iceweasel on Debian
  Squeeze.)  Had to add 'cellspacing' attribute to some tables,
  since IE versions < 8 do not support 'border-spacing' property.

inveniosoftware/invenio-base,tiborsimko/invenio-base,inveniosoftware/invenio-base,tiborsimko/invenio-base