[mythtv] underscan OSD only

[Jim Paris]

> I think if you could set parameters for the OSD rectangle
> independently from (or I guess it would be more like 'scaled
> to' =) the playback overscan settings or the aspect ratio
> mode, that could be used as a common solution for aspect mode,
> CC position and OSD in general.

OK, what if we break all of the sizings into a new setup category,
Geometry, that contains sections:

GUI ("Geometry of main user interface and menus")
  - Fullscreen
    OR
  - Specify x, y, w, h

Video ("Geometry of video playback window")
  - Fullscreen
    OR
  - Same as GUI
    OR
  - Specify x, y, w, h

OSD ("Geometry of on-screen overlay during video playback")
  - Fullscreen
    OR
  - Same as GUI
    OR
  - Same as Video
    OR
  - Specify x, y, w, h

Video Overscan ("Grow or shrink the video inside its window")
  - Specify h, v percentage and x, y offset

.. with a note that Video and Video Overscan don't work on a PVR-350.

There are a couple different ways the aspect ratios could fit into
this; not sure which is best at the moment.

Sound reasonable?

-jim