revert mistake in commit 78db874b

Extra header is stored at &ogg_header + (1 * sizeof(ogg_header)),
not &ogg_header + (sizeof(ogg_header) * sizeof(ogg_header)).

  - make it a bit simpler to read
  - add a shortcut to "Open skin.."
    (Ctrl-Shift-S chosen instead of Ctrl-S, since the latter
    is already used elsewhere)
  - Reuse the full version of "Open Media" with all accelerators
    being displayed instead of the light version
  - add the Help menu

With this new enriched popupmenu, skins2 should now offer all major
vlc hotkeys, which users have been asking for repeatedly.

Signed-off-by: Martin Storsjö <martin@martin.st>

Signed-off-by: Rafaël Carré <funman@videolan.org>

Using both PCR and ES PTS seems to cause problems in some cases