MovieInfo renderer: allow to show full pathname

- MetaDescription only showed short description. Skins use Event info for
  recordings to show some usefull info. But for files without event data
  nothing was shown.
  In this change MetaDescription will check for event info, short
  description and full file pathname to get some usefull info.
  SKins can now use MovieInfo MetaDescription instead of EventName
  extendedDescription
- cosmetics: use defined variables
- Maybe the short description should not check for directories to
  show full pathname anymore ...