Vout rework

• vout needs distinct splitting
  • vout_core (vout_thread)
  • vout_window
  • vout_input (needed when not 1:1 mapping between input and window : wall, clone)
  • pic_filter
  • vout_filter
• needs 'assistance' vout windows (clone filters, goom,subtitles) (property of vout_window). No OSD on these vouts ? or only some ... if only vout present ...
• 4:3, 16:9, freeform Aspect Ratio
• cropping and padding (do at OS level, but provide a core call to set it up and configure).
• OSD at window resolution instead of video res (secondary vout channel - write on output instead of render)
• Use OS native calls where appropriate, with 'C' fallbacks. (OpenGL, Quartz, DirectX already has many of the funtionalities we seek and sometimes they are a lot faster too).
• Allow a vout to reuse a window by resizing it (instead of closing and opening).
• better hotkeys integration : need hotkey module redesign to act on selected vout and relevant input instead of the first we find

This still doesn't allow everything. if we really want to be "SICK", we could allow for mp4 style composited output. (let's not do this though :D )